Chapter 4: Matter and Heat

1
Chapter 4 Matter and Heat

• Alyssa Jean-Mary
• Source The Physical Universe by Konrad B.
  Krauskopf and Arthur Beiser

2
Matter

• All matter is made up of billions of tiny
  separate particles whether it is a solid, a
  liquid, or a gas
• These particles are in constant random motion
  the kinetic energy of this motion is what
  constitutes heat

3
Temperature and Heat

• If something is at a higher temperature, it
  contains more heat
• However, if two objects are at different
  temperatures, the object at the higher
  temperature doesnt necessarily have more heat
  than the object at the lower temperature just
  because it is at a lower temperature
• If there is more of an object with a lower
  temperature, it has more heat than less of the
  same object with a higher temperature
• Also, if there are two objects with the same mass
  (i.e. the same amount), even if they are at the
  same temperature, they might have different
  amounts of heat

4
Temperature and Thermometers

• Temperature is a physical quantity that means
  something in terms of sense impressions i.e.
  temperature is something that gives rise to
  sensations of hot and cold
• A thermometer is a device used to measure
  temperature
• The thermometers that we use everyday are based
  on the principle that when most substances are
  heated, they expand, and when most substances are
  cooled, they shrink in other words, they are
  based on the fact that different materials react
  differently to the same amount of temperature
  change
• Mercury-in-glass thermometers work because
  mercury expands more than glass when heated to
  the same temperature and it shrinks more than
  glass when cooled to the same temperature. Thus,
  the length of mercury in the thermometer
  indicates the temperature i.e. a greater height
  of mercury means a higher temperature, and a
  lower height of mercury means a lower temperature
• Bimetallic strip thermometers contain two
  different kinds of metals that expand at
  different rates. When these thermometers are
  exposed to hot and cold, they bend in different
  directions. At higher temperatures, the metal
  that expands more is on the outside of the curve,
  and at lower temperatures, the metal that shrinks
  more is on the outside of the curve, thus bending
  the strip in the opposite direction. The exact
  amount of bending in either direction determines
  the temperature. These strips are used in
  thermostats that switch on and off heating
  systems, refrigerators, and freezers when certain
  preset temperatures are reached.
• Thermometers can also be based on the principle
  that the color and amount of light that is
  emitted by an object varies with the temperature
  of the object
• For example, a poker that is thrust into a fire
  first glows dull red. It then glows bright red,
  orange, yellow, and finally, white, if it reaches
  a high enough temperature.
• This principle is what astronomers use to
  determine the temperature of stars

5
Temperature Scales

• On the Celsius scale, the freezing point of water
  is 0C and the boiling point of water is 100C
• On the Fahrenheit scale, the freezing point of
  water is 32F and the boiling point of water is
  212F
• This scale is used in only a few English-speaking
  countries (the same countries that still use the
  British system of units)
• To convert between Fahrenheit temperatures (TF)
  to a Celsius temperatures (TC), use the following
  equations
• TF (9/5)TC 32 (to convert from TC to TF)
• TC (5/9)(TF 32) (to convert from TF to TC)
• Normal body temperature is 98.6F on the
  Fahrenheit scale and 37.0C on the Celsius scale

6
Example Calculations of Temperature Conversions

• Converting TF to TC Example What is 56F in
  degrees Celsius?
• Answer
• TC (5/9)(TF 32)
• TC (5/9)(56 32) 13.3C

• Converting TC to TF Example What is 324C in
  degrees Fahrenheit?
• Answer
• TF (9/5)TC 32
• TF (9/5)(324) 32 615.2F

7
Heat

• The heat of a body of matter is the sum of the
  kinetic energies of all the separate particles
  that make up the body
• The more kinetic energy the particles contain,
  the more heat the body has, and the higher the
  bodys temperature.
• The amount of heat that a body contains is called
  its internal energy
• Since heat is a form of energy, the SI unit of
  heat is the Joule
• The nature of the substance determines how much
  heat is needed to raise or lower the temperature
  of 1kg of the substance by 1C. Liquid water
  needs more heat to change its temperature than
  almost any other substance. For water, it takes
  4.2kJ of heat to raise the temperature of 1kg of
  water by 1C. In contrast, gold only takes 0.13kJ
  of heat to raise the temperature of 1kg of gold
  by 1C.
• The specific heat capacity or the specific heat
  (c) of a substance is the amount of heat that
  needs to be added to or removed from 1kg of the
  substance in order to change its temperature by
  1C
• The SI unit for specific heat (c) is kJ/kgC
• Thus, the specific heat for water is 4.2kg/kgC
  and the specific heat for gold is 0.13kJ/kgC.
• Metals have fairly low specific heats. This means
  that only a small amount of heat is needed to
  change the temperature of 1kg of a metal by 1C.
• The equation involving specific heat is
• Q mc?T
• where Q is the amount of heat that is added or
  removed from the substance, m is the mass of the
  substance, c is the specific gravity of the
  substance, and ?T is the change in temperature

8
Example Calculation using Specific Heat

• Example What is the specific heat of a substance
  that required 453kJ to change the temperature
  from 56C to 89C if the mass of the substance is
  96kg?
• Answer
• Given 453kJ, 56C, 89C, 96kg
• Looking for specific heat (c)
• Equation Q mc?T thus, c Q/(m?T) and ?T
  Tf - Ti
• Solution ?T 89C - 56C 33C c
  453kJ/(96kg)(33C) 0.143kg/kgC

9
Heat Transfer

• Three ways to transfer heat from one place to
  another
• Conduction is when heat flows through an object.
  For example, when one end of a poker is placed in
  a fire, the other end gets warm because heat is
  flowing through the poker. This way to transfer
  heat is inefficient.
• Convection happens when a portion of a fluid
  (either a gas or a liquid) is heated, since it
  expands, it becomes lighter than the surrounding,
  colder fluid, and thus rises upward. This is the
  idea that heat rises.
• Radiation consists of electromagnetic waves.
  Light is one of the most common forms of
  radiation. This type of heat transfer occurs in
  space because, since space is virtually empty,
  neither conduction nor convection is possible to
  any real extent. This is how the earth receives
  heat from the sun. The earth also radiates heat
  back into space.

10
Metabolic Energy

• Metabolism is a biochemical process by which the
  energy content of the food an animal eats is
  released
• To express this energy content, the unit used is
  kilocalorie (kcal). A kilocalorie is the amount
  of heat needed to change the temperature of 1kg
  of water by 1C.
• 1 kcal 4.2kJ (kiloJoules)
• The kilocalorie is actually what is referred to
  when a dietician uses the term calorie.

11
Maximum Power Output from Metabolic Energy 1

• An animal converts about 10 to 20 percent of its
  metabolic energy to mechanical energy through
  muscular activity
• The rest of its metabolic energy goes into heat
  energy, most of which escapes through the skin of
  the animal
• The maximum power output that an animal is
  capable of depends on its maximum metabolic rate.
  The maximum metabolic rate depends on an animals
  ability to release the resulting heat, which
  depends on the animals surface area.
• Thus, since a larger animal has a larger surface
  area than a smaller animal, it has a higher
  maximum power output because it has a greater
  ability to release the resulting heat, which
  means that it has a higher maximum metabolic
  rate. But, since a larger animal also has more
  mass than a smaller animal, its metabolic rate
  per kilogram decreases because an animals mass
  goes up faster with its size than its skin area
  does.
• African elephants partly overcome this limitation
  of a small surface-area-to-mass ratio because of
  their enormous ears. Their ears help them get rid
  of metabolic heat.
• Most birds are small because if the size of a
  bird increases, its metabolic rate per kilogram
  (along with its power output since they are
  directly related) deceases even though the amount
  of work needed to perform per kilogram to fly
  stays the same. This is way large birds (i.e.
  ostriches and emus) are not noted for their
  flying ability

12
Maximum Power Output from Metabolic Energy 2

• Some typical basal metabolic rates (i.e. rates
  that correspond to an animal resting) are
• For a person, 1.2W/kg
• For a cow, 0.67 W/kg
• For a pigeon, 5.2 W/kg
• When an animal is active, its metabolic rate is
  much higher than when the animal is resting (i.e.
  when it is at its basal rate)
• For example, a 70-kg person has a basal rate of
  about 80W. When performing light work while
  sitting, the persons rate will be about 125W.
  When the person is walking, the rate will be
  about 300W, and when the person is running hard,
  the rate could be as much as 1200W.
• The highest metabolic rate per kilogram are in
  the flight muscles of insects
• In addition to the muscles using energy, the
  brain of an animal also uses energy to function
• A persons brain uses about 20 to 25 percent of
  the metabolic energy the person has.
• A monkeys brain uses about 9 percent of the
  metabolic energy the monkey has.
• A cats brain and a dogs brain use about 5
  percent of their metabolic energy.
• If the amount of energy from food a person has is
  greater that a persons metabolic needs, then the
  excess energy goes into additional tissue. If the
  person is active, then the excess energy goes
  into muscle. If not, then the excess energy goes
  into fat. The energy that is stored in fat can be
  used later if the amount of energy from food is
  not enough for a persons metabolic needs.

13
Fluids

• Solids have a definite size and shape. Their
  particles vibrate around fixed positions.
• Liquids have a definite size (i.e. volume), but
  they dont have a definite shape because they
  flow to fit the container they are in. Their
  particles are about as far apart as those of
  solids, but they are able to move about.
• Gases dont have a definite size or shape they
  fill whatever container they are in. Their
  particles are able to move about freely.
• Fluids are substances that can flow readily.
  Liquids and gases are therefore called fluids.

14
Density

• The density of a substance is its mass per unit
  volume
• density mass/volume OR d m/V
• When a metal is referred to as heavy as opposed
  to light, what is meant is that the metal has a
  high density
• The proper SI unit of density is kg/m3 (kilograms
  per cubic meter), but it is usually expressed in
  g/cm3 (grams per cubic centimeter), where 1 g/cm3
  1000 kg/m3

15
Example Calculation of Density

• Example What is the density of an object that
  measures 3.4 cm by 23.5 cm by 5.7 cm and has a
  mass of 432 g?
• Answer
• Given 3.4cm, 23.5cm, 5.7cm, 432g
• Looking for density (d)
• Equation d m/V, V LxWxH
• Solution V (3.4cm)(23.5cm)(5.7cm) 455.43cm3
  and thus, d 432g/455.43cm3 0.949g/cm3

16
Pressure

• Pressure is the ratio between the force acting
  perpendicular on an object and the area of the
  object
• Pressure force/area OR P F/A
• The SI unit of pressure is the Pascal (Pa),
  where, since force is expressed in Newton (N) and
  area is expressed in m2, Pa N/m2
• The SI unit Pascal was named after the French
  scientist and philosopher Blaise Pascal
• Since the Pascal is a very small unit (i.e. the
  amount of pressure that your thumb exerts by
  pushing really hard on a table is about
  1,000,000Pa), the unit kPa (kiloPascal) is
  usually used, where 1 kPa 1000 Pa 0.145lb/in2

17
Example Calculation of Pressure

• Example What is the pressure on an object that
  has a force of 56N applied to it and an area of
  32m2?
• Answer
• Given 56N, 32m2
• Looking for pressure (P)
• Equation P F/A
• Solution P 56N/32m2 1.75Pa

18
Pressure in a Fluid

• For fluids, pressure is useful because
• The forces that a fluid exerts on the walls of
  its container and those that the walls exert on
  the fluid always act perpendicular to each other
• The force exerted by the pressure in a fluid is
  the same in all directions at a given depth
• An external pressure exerted on a fluid is
  transmitted uniformly throughout the fluid
• Because fluids have these properties, if we have
  a tube with a fluid in it, and we apply a
  pressure with a pump to the fluid at one end of
  the tube, we can transmit the force to the fluid
  at the other end of the tube that will then
  transmit the force to push against a movable
  piston. Thus, we can transmit a force from one
  place to another.
• If the fluid used in a machine to transmit forces
  is a liquid, the machine is called hydraulic.
• If the fluid used in a machine to transmit forces
  is a gas, the machine is called pneumatic.

19
Pressure and Depth

• Inside a pump, the air at the bottom of the
  cylinder is under a greater amount of pressure
  than the air at the top of the cylinder because
  of the weight of the air in the cylinder.
• In a tire pump, this pressure difference is never
  small
• At sea level on the earth, there is an average of
  101 kPa (15 lb/in2) of pressure due to the weight
  of air above us. This amount of pressure
  corresponds to 10.1N on every square centimeter
  of our bodies. We are not aware of this extreme
  pressure because the pressures inside our bodies
  are the same.
• A barometer is used to measure atmospheric
  pressure.
• If the depth increases, the pressure also
  increases.
• Thus, most submarines cant go under the water
  more than a few hundred meters without the danger
  of collapsing.
• At a depth of 10 km in the ocean, the amount of
  pressure is about 100 times greater than the
  amount of pressure at sea level, which is enough
  pressure to compress water by about 3 percent of
  its volume. The fish that live at these depths
  survive just like we do at sea level i.e.
  because their inside pressures are the same as
  the outside pressure.
• Scuba divers carry tanks of compressed air with
  regulator valves, which allow the air to be at
  the same pressure as the water around them. Scuba
  stands for Self-Contained Underwater Breathing
  Apparatus. As a diver is returning to the
  surface, the diver must constantly breathe out to
  allow the air pressure in the lungs to decrease
  at the same rate as the pressure of the water is
  decreasing. If this is not done, the pressure
  difference between the lungs and the water might
  burst the lungs. This is the same principle that
  is in effect when deep-sea fish explode when they
  are brought too fast to the surface of the water.

20
Buoyancy

• If an object is in a fluid, there is an upward
  force acting on it due to the fact that pressure
  increases with increasing depth. Because of this
  (i.e. that the pressure is greater at larger
  depths), the upward force on the bottom of the
  object is greater than the downward force on its
  top. The difference between these two forces is
  called the buoyant force.
• An object floats when its buoyant force is
  greater than its weight, and it sinks if its
  buoyant force is less than its weight.
• For example, balloons float in air and ships
  float on the sea because their buoyant forces are
  greater than that of their weights.

21
Archimedes Principle

• A body of water is immersed in a tank of water.
  This body of water is supported by a buoyant
  force Fb that is equal to its weight, wwater
  dVg. The buoyant force is the result of all the
  forces from all the water that is in the tank
  acting on this body of water. This buoyant force
  is always upward because the pressure under the
  body of water is always greater that the pressure
  above it, while its weight is always a downward
  force. The forces on the sides of the body of
  water cancel each other out.
• A solid object has a volume V and is in the same
  size and shape tank as the tank of water that the
  body of water is in. The forces on the object are
  the same as the forces on the body of water.
  Thus, Fb dVg, where d is the density of the
  fluid, V is the volume of fluid that is displaced
  by the object, and g is the acceleration of
  gravity (9.8m/s2).
• Archimedes Principle Buoyant force on an
  object in a fluid weight of fluid displaced by
  the object
• Archimedes Principle holds whether an object
  floats or sinks. An object floats if its weight
  is less than the buoyant force, and it sinks if
  its weight is greater than the buoyant force.
  When an object is floating, only the part of the
  object that is actually in the water is used to
  calculate the volume.
• If an object floats in a fluid, that means that
  its average density is lower than the density of
  the fluid. Even though the density of steel is
  higher than the density of water, a steel ship
  floats because it is a hollow shell, so
  therefore, the average density of the ship is
  actually lower than the density of water even
  though it is made out of steel, and even when the
  ship is loaded with cargo. If the ship gets a
  leak and starts to take on water, the average
  density of the ship starts to increase, and thus,
  the ship starts to sink.

22
Example Calculation of Buoyant Force

• Example What is the buoyant force on an object
  if it is in a fluid with a density of 2.3kg/m3
  and displaces a volume of 45m3 of the fluid?
• Answer
• Given 2.3kg/m3, 45m3
• Looking for buoyant force (Fb)
• Equation Fb dVg
• Solution Fb (2.3kg/m3)(45m3)(9.8m/s2)
  1014.3N

23
Boyles Law

• When the temperature of a gas is held constant,
  if the pressure on the gas is doubled, the volume
  of the gas is halved - in other words, the
  pressure and the volume of a gas are inversely
  proportional to each other (i.e. if one
  decreases, the other one increases by the same
  proportion), as long as the temperature is held
  constant
• As an equation, Boyles Law is
• p1/p2 V2/V1 (at constant temperature)
• where p1 is the initial pressure, p2 is the
  final pressure, V1 is the initial volume, and V2
  is the final volume
• Another version of the equation is
• p1V1 p2V2

24
Example Calculations using Boyles Law

• Example 1 What is the final volume of a gas that
  started with a volume of 45L under a pressure of
  2.3atm if 5.7atm is now applied to it?
• Answer
• Given 45L, 2.3atm, 5.7atm
• Looking for final volume (V2)
• Equation p1V1 p2V2 - thus, V2 p1V1/p2
• Solution V2 (2.3atm)(45L)/(5.7atm) 18.2L

• Example 1 How much pressure is applied to a gas
  that started with a volume of 900L under a
  pressure of 24.3atm if it now has a volume of
  48L?
• Answer
• Given 900L, 24.3atm, 48L
• Looking for final pressure (p2)
• Equation p1V1 p2V2 thus, p2 p1V1/V2
• Solution p2 (24.3atm)(900L)/(48L) 455.6atm

25
How Temperature Changes Affect Volume and Pressure

• When the pressure of a gas is held constant, if
  the temperature of the gas is increased, the
  volume of the gas is also increased AND if the
  temperature of the gas is decreased, the volume
  of the gas is also decreased. Thus, the
  temperature and the volume of a gas are directly
  proportional.
• Instead, when the volume of a gas is held
  constant, if the temperature of the gas is
  increased, the pressure of the gas is also
  increased AND if the temperature of the gas is
  decreased, the pressure of the gas is also
  decreased. Thus, the temperature and the pressure
  of a gas are directly proportional.

26
Absolute Zero

• On the Celsius scale, absolute zero is at -273C
• At absolute zero, if the volume of a gas was held
  constant, the pressure of the gas would be zero.
  Also, at absolute zero, if the pressure of a gas
  was held constant, the volume of the gas would be
  zero
• It is unlikely that experiments will ever reach a
  temperature of absolute zero for two reasons
• 1. It is impossible to reach such a low
  temperature.
• 2. All known gases turn to liquids before they
  reach this low temperature.
• The absolute temperature scale is another scale
  that is used to give temperatures (in addition to
  the Fahrenheit scale and the Celsius scale). This
  scale begins at absolute zero and is given as
  degrees Celsius above absolute zero. Therefore, a
  Celsius temperature (TC) can be converted into an
  absolute temperature (TK) using TK TC 273
• On this scale, the freezing point of water is
  273K (K Kelvin for English physicist Lord
  Kelvin) and the boiling point of water is 373K

27
Charless Law

• Charless Law says that the volume of a gas is
  directly proportional to the absolute temperature
  of the gas
• As an equation, Charless Law is
• V1/V2 T1/T2 (at constant pressure)
• where V1 is the initial volume, V2 is the final
  volume, T1 is the initial temperature in K
  (absolute temperature), and T2 is the final
  temperature in K (absolute temperature)
• Another version of the equation is
• V1/T1 V2/T2

28
Example Calculations using Charless Law

• Example 1 What is the final volume of a gas that
  started with a volume of 97L at a temperature of
  35C if it is heated to 56C?
• Answer
• Given 97L, 35C, 56C
• Looking for final volume (V2)
• Equation V1/T1 V2/T2 - thus, V2 V1T2/T1 and
  TK TC 273
• Solution TK 35C 273 308K TK 56C 273
  329K thus, V2 (97L)(329K)/(308K) 103.6L

29
The Ideal Gas Law

• Boyles Law and Charless Law are combined to
  form the ideal gas law
• p1V1/T1 p2V2/T2
• At constant temperature, T1 T2, and the
  equation becomes Boyles Law
• At constant pressure, p1 p2, and the equation
  becomes Charless Law
• Another version of the ideal gas law is
• pV/T constant
• This version of the ideal gas law shows that
  these quantities as a whole dont change in value
  for a gas sample even if the individual
  quantities (i.e. p, V, or T) may change.

30
Example Calculation using the Ideal Gas Law

• Example What is the final temperature of an
  object that was initially at a pressure of
  4.5atm, a volume of 345L, and a temperature of
  90C, if it is now under a pressure of 3.2atm
  with a volume of 65L?
• Answer
• Given 4.5atm, 345L, 90C, 3.2atm, 65L
• Looking for final temperature (T2)
• Equation p1V1/T1 p2V2/T2 - thus, T2
  p2V2T1/p1V1 and TK TC 273
• Solution TK 90C 273 363K thus, T2
  (3.2atm)(65L)(363K)/(4.5atm)(345L) 48.6K

31
The Kinetic Theory of Matter

• The kinetic theory of matter involves a simple
  model that accounts for many physical and
  chemical properties of matter.
• This model says that all matter is composed of
  tiny particles.
• For a gas, these particles are referred to as
  molecules, which are substances that consist of
  two or more atoms.
• For liquids and solids, the particles can be one
  of three types molecules, atoms, or ions.

32
The Kinetic Theory of Gases

• The sizes, speeds, and shapes of the molecules of
  many kinds of matter are known today
• For example, a molecule of Nitrogen, which is the
  chief constituent of air, is about 1.8 x 10-10m
  across. It has a mass of about 4.7 x 10-26kg. At
  0C, its average speed is about 500m/s, which is
  about the speed of a rifle bullet. Every second a
  molecule of Nitrogen collides with more than a
  billion other molecules. Most of the other
  constituents of air have a similar size and speed
  to that of Nitrogen. For every cubic centimeter
  of air, there are 2.7 x 1019 other molecules
  present. To get an idea of how many molecules
  this is if all of the molecules that are present
  in a cubic centimeter of air were divided equally
  amount 6.3 billion people, each person would have
  over 4 billion molecules of air.

33
The Three Basic Assumptions of the Kinetic Theory
of Gases

• There are three basic assumptions that apply to
  the Kinetic Theory of gases
• 1. Gas molecules are small compared to the
  average distance between them.
• 2. Gas molecules collide with each other without
  losing kinetic energy.
• 3. Gas molecules exert almost no force on one
  another, except when they collide with each
  other.
• These assumptions have been verified by
  experimentation
• These assumptions show us that a gas is mainly
  empty space in which isolated particles are all
  moving around in different directions. Therefore,
  we can compare a gas to a swarm of angry bees
  that is in a closed room. Each molecule collides
  with other molecules about billions of times a
  second. Theses collisions change the speed and
  direction of the molecule, but when they arent
  colliding, they are unaffected by their
  neighbors. There is no order to the motion of
  these objects. They have no uniform speed or
  direction. All that can be said about the
  molecules is that they have an average speed and
  that, at any given instant, there are as many
  molecules moving in one direction as there are
  molecules moving in the opposite direction.
• If a molecule comes to a rest momentarily, it
  will not stay that way long i.e. another
  molecule will soon collide with it to send it
  back into motion.
• Also, if a molecule reaches a speed than the
  average speed of the molecules, it will not stay
  that way long either i.e. other collisions will
  slow its speed.

34
Properties of Gases from the Kinetic Theory of
Gases

• Gases can expand and even leak through a small
  opening because of their rapid movement and the
  fact that they dont have a strong attraction for
  each other
• Gases can be easily compressed because on
  average, there molecules are far apart from each
  other
• One gas will mix with another gas because, since
  the molecules are far apart from each other,
  there is plenty of space in between them for
  other molecules
• The mass of a certain volume of a gas is much
  less than the mass of the same volume of a liquid
  or a solid because a gas is mainly empty space

35
The Origin of Boyles Law

• A gas exerts a pressure on the walls of its
  container because the billions and billions
  molecules of the gas consistently hit the
  container. When we measure these billions and
  billions of tiny, separate hits of the molecules,
  what we see is that a continuous force is
  affecting the walls of the container.
• The Kinetic Theory of Gases accounts for Boyles
  Law, which states that p1V1 p2V2 when the gas
  is at constant temperature
• Think of the molecules of a gas in a cylinder as
  some moving vertically (i.e. in between the
  piston and the bottom of the cylinder) and as
  some moving horizontally (i.e. in between the
  walls of the cylinder) the molecules are moving
  equally in either direction. Now, if the piston
  is raised, which doubles the volume of the gas,
  the molecules that are moving vertically are
  going to have to travel further, which means that
  they will not hit the piston or the bottom of the
  container as much as they used to they will
  actually hit the container half as much. The
  molecules moving horizontally will also have to
  change their bombardment of the walls of the
  container because now they have more of the walls
  to interact with. Since these molecules will need
  to hit an area that is twice as big as before,
  the number of hits on the walls of the container
  will decrease just as those for the molecules
  with vertical motion did. This shows that the
  pressure in all parts of the cylinder (vertical
  and horizontal) is cut in half when the volume is
  doubled, which is what Boyles Law predicts. This
  can be expanded to a real gas that has molecules
  that are moving in random motion.

36
Molecular Motion and Temperature

• A fourth assumption is added to the Kinetic
  Theory of gases
• 4. The absolute temperature of a gas is
  proportional to the average kinetic energy of the
  molecules of the gas
• This assumption was added to account for the
  behavior of a gas with a change in temperature
• Since this shows that temperature is related to
  the energy of the molecules, it also is related
  to the speed of the molecules. Thus, if the
  pressure inside a container increases, the
  temperature inside that container also increases.
  This is because when the pressure increases, the
  molecules must be hitting the walls of the
  container with more force, which means that they
  are moving faster.
• Earlier, we saw that if the temperature of a gas
  is at 0K (or -273C), the pressure of the gas is
  at zero. For this to occur, the bombardment of
  the molecules must stop completely. So, at 0K
  (i.e. absolute zero), the molecules of a gas
  would lose all of their kinetic energy. (This is
  a simplified idea since in reality, even at 0K,
  there will be a small amount of KE that will
  never be able to disappear.) The reason that
  there is no temperature below 0K is that there is
  simply no way to have less than no kinetic
  energy. Thus, if there is constant volume, an
  increase in the pressure of the gas will increase
  the temperature of the gas, and if there is
  constant pressure, an increase in the volume of
  the gas will increase the temperature of the gas.

37
The Origin of Charless Law

• When a gas is compressed, since the temperature
  of the gas is the measure of the average kinetic
  energy of the molecules of the gas, the
  temperature in the cylinder should rise
• Put a gas in a cylinder with a piston on top.
  When the piston is moving down, thus increasing
  the pressure inside the cylinder, the molecules
  rebound from the piston with an increase in
  energy, which causes an increase in the
  temperature of the gas. This can be shown when
  using a bicycle tire pump after you have used
  the pump for awhile, you will notice that it gets
  warmer because of the compression of the gas
  inside as the pump is being used. Also, when the
  piston is moving up, which decreases the pressure
  inside the cylinder, the molecules will give up
  some of their kinetic energy to the piston, which
  will cause the temperature of the gas to
  decrease.
• Thus, as a gas expands, it cools. This can
  explain the formation of clouds from rising moist
  air.
• As moist air is moving upward, since the
  atmospheric pressure is decreasing, the water
  vapor in the moist air is cooling, until it
  condenses into the water droplets that constitute
  clouds.

38
Liquids and Solids Intermolecular Forces

• If you compare a gas to a swarm of angry bees,
  then a liquid is bees in their hive, crawling
  constantly over one another.
• The molecules in a liquid slide past one another
  easily, which is why liquids flow. Liquids flow
  less readily than gases do because of the
  intermolecular attractions that act only over
  short distances.
• The molecules in a solid are held together with a
  stronger force than those that hold together
  liquids. Actually, this force is so strong that
  the molecules of solids are not free to move
  about. The molecules of solids still move,
  however they vibrate back and forth rapidly
  between the particles that they are in between,
  as if they were on a spring. This spring
  represents the bond that is between two
  molecules. This bond is electrical in nature.
• The reason why a solid is elastic is because
  after the molecules have been pulled apart or
  pushed together by some force, the molecules
  return to their original positions, with the
  normal amount of space between the molecules
  instead of too much or too less. A force that is
  too great may deform the solid permanently. When
  this occurs, the molecules move to new normal
  positions and find new molecules to bond with. A
  solid can actually break apart if too much force
  is applied.

39
Evaporation Changing a Liquid into a Gas

• A liquid is placed in an open container. The
  molecules of the liquid are moving in all
  directions in the dish, some moving faster than
  others. Some of the molecules are moving fast
  enough upward to escape into the air. They escape
  into the air even though they have an attraction
  to their neighbor molecules because the
  attraction is not enough to stop them from
  escaping. This loss of molecules to the air is
  referred to as evaporation. Since it is the
  faster molecules, and thus, the warmer molecules
  that escape into the air, the slower molecules
  are left behind in the liquid, which makes the
  liquid cool.
• If you compare the evaporation of water to
  alcohol, you see that alcohol evaporates more
  quickly than water, and thus, cools more quickly
  than water. This is because the attraction liquid
  alcohol molecules have for one another is less
  than the attraction liquid water molecules have
  for one another, and thus a greater number of
  alcohol molecules can escape.

40
Boiling Changing a Liquid into a Gas

• When a liquid is heated, at a certain
  temperature, even molecules that are traveling at
  average speed (i.e. not only the molecules that
  are traveling at high speeds) can overcome the
  attraction between their neighbor molecules and
  escape into the air. At this temperature, there
  are bubbles of gas throughout the liquid, and
  thus, the liquid is boiling. Therefore, this
  temperature is referred to the boiling point of
  the liquid.
• The boiling point of water is 100C, which is
  higher than the boiling point of alcohol, which
  is 78C. This reinforces the idea that alcohol
  evaporates more quickly than water.
• Evaporation and boiling differ in the following
  two ways
• 1. Evaporation occurs only at the surface of the
  liquid, whereas boiling occurs throughout the
  entire liquid.
• 2. Evaporation occurs at all temperatures,
  whereas boiling only occurs at the boiling point
  or temperatures above the boiling point.

41
Heat of Vaporization

• To change a liquid to a gas, whether by
  evaporation or boiling, energy is needed
• For evaporation, the energy is supplied from the
  heat content of the liquid itself, which is why
  the liquid that is left behind is cooler
• For boiling, the energy is supplied from heat
  from an outside source
• The heat of vaporization of a substance is the
  amount of energy that is needed to change each
  kilogram of liquid into gas at its boiling point
• For water at its boiling point, 100C, the heat
  of vaporization is 2260kJ
• The temperature of a liquid and its gas are not
  different. Because of this, the kinetic energy
  that the liquid has is the same amount of kinetic
  energy that its gas has. Thus, the extra energy
  that is supplied to the liquid to turn it into a
  gas does not go into the kinetic energy of the
  gas. Because the molecules in a liquid are closer
  together, the intermolecular forces in a liquid
  are stronger than those in a gas. In order to
  change a liquid into a gas, the molecules of the
  liquid have to be broken apart and moved so that
  they are in positions that are far apart from
  each other, and thus have smaller attractions for
  each other. This requires that the strong forces
  between molecules in a liquid need to be
  overcome. The molecules of the liquid that are
  moving apart to become gas molecules are gaining
  potential energy, just like a stone that is
  thrown upward against the earths gravity gains
  potential energy, except this is potential energy
  with respect to intermolecular forces. Thus, the
  extra energy that is supplied to the liquid to
  turn it into a gas becomes potential energy of
  the gas.
• When the reverse occurs, i.e. when a gas becomes
  a liquid, instead of the liquid molecules
  escaping from the liquid into the air, the gas
  molecules are falling toward one another because
  of their attraction to one another. When this
  occurs, the potential energy that the gas
  molecules are losing is taken up as heat by the
  surroundings.

42
Melting Changing a Solid into a Liquid

• Heat is needed to change a solid into a liquid at
  its melting point, just like heat is needed to
  change a liquid to a gas at its boiling point
• The heat of fusion of a substance is the amount
  of heat that is needed to change each kilogram of
  solid into liquid at its melting point
• For water at its melting point, the heat of
  fusion is 335kJ/kg
• Most other substances have a lower heat of fusion
  than water
• The same amount of heat that is needed to change
  one kilogram of a solid to a liquid has to be
  released in order to change one kilogram of a
  liquid into a solid
• The heat of fusion of a substance is always much
  smaller than the heat of vaporization of the
  substance
• The molecules of a solid are arranged in such a
  way that they have the maximum amount of force
  between themselves and their neighbors. To become
  a liquid, the molecules of a solid have to become
  more random, to be able to move about more. To do
  this, energy needs to be added so that the forces
  between the molecules of a solid are overcome.
  But, the amount of energy that is needed to do
  this is not as much as for a liquid to become a
  gas since a liquid still has a definite volume,
  even if it doesnt have a definite shape, unlike
  a gas, which has no definite shape or volume.
  Since the molecules of a gas are so far apart,
  they move more freely and thus, can expand. In a
  vacuum, the molecules of a gas could expand
  indefinitely.

43
Water

• If we start with 1kg of ice at -50C, and we add
  heat, the ice will increase in temperature until
  0C (i.e. the melting point of water), which is
  when it will start to melt. The temperature will
  remain at 0C until all of the ice has melting.
  After all of the ice has melted, and thus, has
  become water, the temperature of the water will
  increase until 100C (i.e. the boiling point of
  water) is reached, which is when it will start
  boiling. The amount of energy that is required at
  this point (i.e. to turn the water into steam) is
  a lot more than the amount of energy that was
  required to melt the ice. The temperature will
  remain at 100C until all the water has become
  steam, and then, the temperature of the steam
  will rise since more heat is still being added.

44
Sublimation

• Sublimation occurs when a solid turns directly
  into a gas, without first turning into a liquid.
• Most substances will sublime as long as the right
  conditions of temperature and pressure are
  present.
• Usually pressures well under atmospheric pressure
  are needed in order for sublimation to occur.
• One example of an exception is solid carbon
  dioxide, which is also referred to as dry ice.
  Solid carbon dioxide sublimes (i.e. turns into a
  gas) at temperatures above -79C, even if it is
  at atmospheric pressure
• Instant coffee can be made using sublimation.
  Coffee is first brewed, and then it is frozen.
  Following that, it is put into a vacuum chamber.
  The ice that is in the frozen coffee sublimes to
  water vapor, which is pumped away. Freeze drying
  coffee like this doesnt affect the flavor of the
  coffee as much as when you dry it by heating. The
  process of freeze drying is also used to preserve
  many other materials, including blood plasma.

45
Changes of State
46
Energy Transformations

• Remember that any form of energy can be converted
  into another form of energy. This applies to
  heat, since it is a form of energy. The
  conversion of heat to another form of energy does
  not occur efficiently.
• For example, mechanical energy is obtained by
  heat that is given off from burning coal and oil
  in various types of engines. A large amount of
  the heat that is given off does not get changed
  into mechanical energy it is wasted. In an
  electric power station, about two-thirds of the
  heat is wasted. This is a serious situation since
  these loses occur on the raw energy that is
  available to us.
• This inefficient conversion of heat in engines
  was discovered in the nineteenth century, at the
  start of the Industrial Revolution. The loss of
  heat is not due to poor design or construction of
  the engines it is just because heat cant be
  converted to another form of energy without these
  losses. The reasons for this inefficient
  conversion was studied by engineers to get as
  much mechanical energy as they could out of a
  given amount of fuel and by scientists to study
  the properties of heat. What was learned was for
  the idea that heat is actually the kinetic energy
  of random molecular motion.

47
Heat Engines

• Since all that is needed to obtain heat is to
  burn a fuel, heat is an easy and a cheap form of
  energy to obtain
• A heat engine is a device that turns heat into
  mechanical energy
• Some examples of heat engines are the gasoline
  and diesel engines of cars, the jet engines of
  aircraft, and the steam turbines of ships and
  power stations.
• All engines operate in the same basic way a gas
  is heated and then it expands against a piston or
  the blades of a turbine
• When a gas in a cylinder on top of which is a
  piston is heated, since the temperature of the
  gas is increasing, the pressure of the gas is
  increasing, which makes the piston move upward.
  This upward movement is what is used to make use
  of an engine. When the piston reaches the top of
  the cylinder, the conversion of heat into
  mechanical energy stops since the piston stops
  moving. If we want to continue to make use of an
  engine, we need to push the piston back down
  again. Then, we can start another cycle to expand
  the gas.
• If the piston is pushed back down to continue the
  cycle when the gas is still hot, the amount of
  work that needs to be done is the same as the
  amount of energy that was produced by the
  expansion of the gas. This means that if it is
  pushed back down when the gas is still hot, no
  net work will be done. Thus, for some work to be
  done, the gas first must be cooled so that there
  is less work required for the piston to be pushed
  back down. This is where the heat is lost in an
  engine. Thus, if you want an engine to continue
  to work, there is no way to prevent this heat
  loss. The heat that is lost usually ends up in
  the atmosphere around the engine, in the water of
  a nearby river, or in the ocean.

48
The Complete Cycle of Heat Engines

• In the compete cycle of an engine, heat flows
  into and out of the engine. During this process,
  some of the heat is converted into mechanical
  energy.
• In order for an engine to operate, both a hot
  reservoir and a cold reservoir are needed. A gas
  flows naturally from the hot reservoir to the
  cold reservoir.
• In a gasoline or diesel engine, the hot reservoir
  is the burning gases of the power stroke, and the
  cold reservoir is the atmosphere.
• Even though a vast amount of heat is contained in
  the molecular motions of the atmosphere, the
  oceans, and the earth itself, it is only rarely
  used because a colder reservoir is needed for the
  heat to flow into.
• A refrigerator is the reserve of a heat engine.
  It uses mechanical energy to push heat from a
  cold reservoir to a warm reservoir. Energy is
  required for this movement because heat naturally
  flows from a warm reservoir to a cold one. Since
  there is a large amount of energy that is needed
  to drive a refrigerator, it is not a good cold
  reservoir for an engine to use.

49
Thermodynamics

• Thermodynamics is the study of heat
  transformation
• There are two fundamental laws of thermodynamics
• 1. Energy cannot be created or destroyed, but it
  can be converted from one form to another.
• 2. It is impossible to take heat from a source
  and change all of it to mechanical energy or
  work some heat must be wasted.
• As you can see, the first law of thermodynamics
  is actually the law of conservation of energy. It
  basically is saying that we cannot obtain
  anything from nothing.
• The second law of thermodynamics referrers only
  to heat. It says that the conversion of heat into
  another form of energy is inefficient.
• Thermodynamics specifies the maximum efficiency
  of a heat engine only by ignoring the losses to
  friction and some other practical difficulties.
  The maximum efficiency depends only on the
  absolute temperatures of the hot reservoir and
  the cold reservoir by which the engine operates
• Maximum efficiency (work output/energy
  input)maximum
• OR
• Eff(max) 1 (Tcold/Thot)
• where Eff(max) is the maximum efficiency, Tcold
  is the temperature of the cold reservoir, and
  Thot is the temperature of the hot reservoir
• This equation shows that the greater the ratio
  between the two temperatures, the less heat is
  wasted, and therefore, the more efficient the
  engine is.

50
A Steam Turbine

• A steam turbine is what is used in a power
  station. The steam comes from a boiler that is
  heated by either a coal furnace, a oil furnace, a
  gas furnace, or a nuclear reactor. The turbine
  shaft is connected to an electric generator. In a
  typical power station, the steam enters the
  turbine at about 570C (843K) and exits at about
  95C (368K) into a partial vacuum. The maximum
  efficiency of a turbine like this is equal to 1
  (368K/843K) or 0.56, so the maximum efficiency
  is 56 percent. The actual efficiency is less than
  40 percent due to friction and other sources of
  energy loss.

51
Why a Heat Engine Must Be Inefficient

• When a gas in a heat engine is heated, its
  molecules increase their average speed, and thus
  their average kinetic energy
• The problem is that the engine can only use this
  increased energy if the molecules of the gas are
  moving in approximately the same direction as the
  piston or turbine blades, but the gas molecules
  are moving in random directions
• To make the gas molecules move in the same
  direction, a lot of the heat that was added to
  the gas would need to be converted to mechanical
  energy
• It is impossible to do this conversion in a heat
  engine, so only a small amount of the heat that
  is in the gas can be extracted as energy of
  orderly motion

52
The Fate of the Universe

• Even though not all heat energy can be converted
  to another form of energy, other forms of energy
  can entirely be converted to heat
• Because of this, there is an overall tendency
  toward an increase in the heat energy of the
  universe, while the other forms of energy are
  thus decreased
• Some examples
• When coal or oil is burned, chemical energy
  becomes heat
• When a machine is operated, friction turns some
  of its energy into heat
• An electric light bulb emits heat in addition to
  its light
• On earth, most of the lost heat is released into
  the atmosphere, the oceans, and the earth, where
  it is largely unavailable for recovery
• In the universe, from a thermodynamics
  standpoint, the stars, including the sun, are the
  hot reservoir, and everything else, including the
  earth and the moon, etc., is the cold reservoir.
  As time goes on, the stars get colder, and the
  rest of the universe will grow warmer, which
  means that there will be less and less energy
  available for the further evolution of the
  universe. If seen on a molecular level, the order
  will become disorder. If this continues,
  everything in the universe will have the same
  temperature and thus the same amount of average
  energy, which is a condition referred to as heat
  death. This is the only possible fate of the
  universe.

53
Entropy

• Entropy is the measure of the disorder of the
  molecules that make up any body of matter
• For example, liquid water has more entropy that
  ice since its molecules are more randomly
  arranged, and the entropy of steam is greater
  than that of liquid water for the same reason
• If the second law of thermodynamics is rewritten
  in terms of entropy The entropy of a system of
  some kind isolated from the rest of the universe
  cannot decrease.
• Writing the second law like this allows it to be
  applied in an exact way to a variety of systems
• For example, while it is being turned into ice,
  if liquid water would rise from the ground by
  itself, energy would be conserved because the
  heat that is lost by the liquid water to change
  it to ice would be converted to kinetic energy.
  This would conserve energy, and thus obey the
  first law of thermodynamics. This doesnt occur
  because it violates the second law of
  thermodynamics If this was to occur, the entropy
  of the liquid water would decrease, which is
  impossible.
• In some cases, it might seem that the entropy of
  something is decreasing, but the entropy of the
  universe is still increasing
• For example, a plant that is taking carbon
  dioxide and water and converting them to leaves
  and flowers appears to be losing entropy. But, it
  needs sunlight to do this, and in order to
  produce this sunlight, the entropy of the sun is
  increasing. If this increase in entropy of the
  sun is taken into account with the lost entropy
  of the plant, overall the universe in actually
  increasing its entropy
• The second law expressed this way is an unusual
  physical principle
• It applies to assemblies of many particles, not
  to individual particles
• It tells what cannot occur, not what can occur
• It is closely tied to the direction of time
• If an event involves only a few individual
  particles, it is reversible, but if it involves
  many particles, it is not always reversible
  i.e. time never run backwards since it is always
  going in the direction of entropy increase
• For example, a bouncing ball can be played
  forward and backward, and you wouldnt be able to
  tell which is which, but if an egg is broken and
  it is played backward, you would be able to tell
  the difference between backward and forward