Thermodynamics

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Thermodynamics
the study of heat
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Kinetic Molecular Theory
All matter is made up of many tiny particles that
are always in motion. In a hot body, the
particles move faster, and thus have more kinetic
energy than particles in a cooler body.
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Solid Crystal
Attractive forces cause molecules vibrate, but
stay in a fixed position
Liquid
Attractive force is weaker in a liquid - -
molecules are further apart and move about quickly
Gas
Attractive force is very weak in a gas - -
molecules are far apart and move about very
quickly.
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Thermal Energy

• the sum of the energy of all particles that make
  up the object

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Energy Transfer
Conduction

• Particles gain energy from the flame.
• They vibrate faster, and as they collide with
  other particles energy is passed from particle to
  particle.

Convection

• Particles gain energy near heater.
• Warm air above is less dense and easier for
  heated air particles to rise.
• As warm air is rising, cool air from the side
  replaces heated air causing a circular convection
  current.

Radiation

• Radiation is the transfer of energy by
  electromagnetic waves.
• Heat radiation is the infrared portion of the
  electromagnetic spectrum.
• Thermal energy from the sun can travel through a
  vacuum at the speed of light, so no particles are
  needed as in conduction or convection.
• Heat radiation can also travel through gases.

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Temperature and Thermometers
Recall that thermal energy was the total of all
energies in a substance.
Temperature is a measure of the average energy of
the particles that make up a substance.
Figure 2
Figure 1
The thermal energy of figure 2 is twice as much
as figure 1 (double the particles).
However, the temperature of figure 1 and 2 is the
same because temperature is the average of the
energies in the substance.
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Temperature Scales
The Celsius scale is based on the properties of
water. The freezing point of pure water is 0
degrees, and the boiling point as sea level is
100 degrees.
Objects contract as they cool. If we cool an
ideal gas, it will contract into a volume that is
only the size of the molecules at - 273.15 oC.
This is the lowest temperature that an object can
reach and is called Absolute Zero.
The Kelvin temperature scale is based on absolute
zero. Absolute zero is the zero point on the
Kelvin scale and the boiling point of water is
373K. Each interval on this scale is called a
Kelvin, and is equal to the size of one Celsius
degree.
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Temperature Conversion
25oC to Kelvin
K C 273
K 25 273
K 289 K
393 K to Celsius
C K - 273
C 393 -274
C 120 oC
Celsius to Fahrenheit
F 9/5 C 32
F 9/5 (20) 32
F 68 oF
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Try These!
Convert from Celsius to Kelvin
27oC
560oC
-184oC
-273oC
Convert from Kelvin to Celsius
110K
22K
402K
323K
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Thermal Expansion
At the level of atoms and molecules, thermal
expansion occurs because the distance between
molecules increases as their thermal energy
increases.
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Linear Expansion
Solids expand in all directions (length, width,
thickness) when heated, and similarly contract
when cooled. For long, thin objects the change is
most noticeable only in length. The change in
length in one direction is termed linear
expansion.
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Linear expansion depends on several factors
change in temperature, original length, type of
material.

• the warmer the material the greater the linear
  expansion

• the longer the material the greater the linear
  expansion

• different materials have greater linear expansion

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Linear Expansion Formula
L Lo T
where L is the change in length in meters
is the coefficient of linear expansion Lo is
the original length, in metres T is the
temperature change in oC
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Volume Expansion
Just as linear expansion occurs in solids, volume
expansion occurs in liquids and gases. Volume
expansion depends the change in temperature,
original volume, and the type of substance.
V Vo T
where V is the change in volume in m3
is the coefficient of volume expansion Vo is
the original volume in m3 T is the temperature
change
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A steel bridge in Saskatchewan is 380 m long. If
the temperature varies from -40.0 C to 30.0 C,
what is the change in the length of the bridge
for this temperature range?
.32 m
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A gasoline tank in a truck holds 60.0 litres at
20C. If the tank is filled to the top and the
daytime temperature goes up to 45C, how much gas
will overflow?
1.4 L
Expansion Practice
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Heat and Thermal Energy
Heat is defined as the thermal energy that flows
from one object to another due to a difference in
their temperatures. Energy always flows from the
hotter to the cooler object.
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Quantity of Heat
The quantity of heat energy (thermal energy) in a
substance depends on several factors
1. Temperature - the higher the temperature of a
substance, the greater the heat energy present
2. Mass - the larger the mass, the greater the
number of particles with heat energy
3. Substance - different substances vary in their
thermal properties. When you eat a hot pizza, you
burn your tongue on the sauce not the crust. This
thermal property is called specific heat
capacity, and this also determines the amount of
heat energy in a substance.
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Specific Heat Capacity

• the quantity of heat (energy) needed to raise
  the temperature of 1 kg of a substance by 1C.

903 J of energy must be added to raise the
temperature of 1 kg of aluminum by 1C. Therefore
the specific heat capacity of aluminum is 903
J/kgC. Water has a specific heat capacity of
4.2 x 103 J/kgC, which means that it takes 4.2 x
103 J of energy to raise 1kg of water by 1C.
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Temperature can be measured using a thermometer.
However, heat must be calculated using the
formula
Q mcDT
Q is the quantity of heat gained of lost, in
joules m is the mass in kilograms c is the
specific heat capacity in J/kgC T is the
temperature change in C
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Substances with a low specific heat capacity warm
quickly because they need less heat energy for a
given change in temperature. They also give up
their heat quickly. Substances with a high
specific heat capacity take a long time to warm
up and they retain their heat for a long time
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How much heat is needed to raise the temperature
of 2.0 kg of copper from 20.0C to 70.0C?
3.9 X 104 J
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A 1.0 kg aluminum block has an initial
temperature of 10.0C. What will the final
temperature of the aluminum block be if 3.0 x 104
J of heat is added?
Specific Heat practice Lab
43oC
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Heat Exchange and Mixtures
When two substances at different temperatures are
mixed, the amount of heat lost by the warmer
substance equals the amount of heat gained by the
cooler substance - assuming no heat is lost to
the surroundings.
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Heat lost Heat gained
The heat loss from the 100g of 80C water is
gained by the 100g of 20C water resulting in a
final temperature of 50C.
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A 1.0 kg brass block that is 88C is placed in
0.44 kg of water at 6C. The final temperature of
the the water and brass is 20C. What is the
specific heat capacity of the brass block?
3.8 X 102 J/kgoC
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A .0400 kg block of zinc at 115C is placed in
.500 kg of water at 15.0C. If the specific heat
of zinc is 388 J/kgC, find the final temperature
of the mixture.
15.7oC
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Calorimeters
Calorimeters are special containers used to
measure the exchange of heat when substances are
mixed. The name comes from the old unit of
energy, the calorie.
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A 0.500 kg piece of lead at 100C is placed in
0.200 kg of water at 20C which is contained in
an aluminum calorimeter that has a mass of 0.400
kg. If the final temperature of the lead, water,
and calorimeter is 24C, find the specific heat
of the lead.
1.3 X 102 J/kgoC
Heat Exchange practice
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Latent Heat and Change of State
Adding or removing heat does not always result in
a change of temperature. During a change of
state, the heat added is called latent heat
because there is no change in temperature. Latent
means "hidden".
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In order for a change of state to occur, solid to
liquid to gas, heat must be added. The addition
of heat causes the particles to move faster,
eventually overtaking the forces that are holding
them together. They become free enough to slide
past each other.
When a substance is melting, all of the added
thermal energy goes into overcoming the forces
holding the particles together. Because there is
no increase in kinetic energy of the particles
there is no increase in temperature.
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Latent heat of fusion is the amount of heat
required to melt 1 kg of a substance without
changing its temperature.
The heat required to melt a solid of mass, m is
given by
Q mHf
Latent heat of vaporization is the amount of heat
required to vaporize 1 kg of a substance without
changing its temperature.
The heat required to vaporize a liquid of mass,
m is
Q mHv
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How much heat energy is needed to change 2.0 kg
of ice at 0C to water at 0C?
6.6 X 105 J
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How much heat energy is needed to change 0.50 kg
of water at 100C to steam at 100C?
1.2 X 106 J
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How much heat does a refrigerator need to remove
from 1.5 kg of water at 20.0 C to make ice at
0C?
6.2 X 105 J
Applications
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