States of Matter and Gas Laws

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• States of Matter and Gas Laws

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Chemical Kinetics

• Study of the reaction mechanisms and the rates of
  reactions.

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Collision Theory

• For a reaction to occur between two particles,
  these particles must collide.

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Collision Theory

• The collision must be
• A. of enough energy
• B. of proper orientation

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Collision Theory

• Most reactions occur in a series of steps.

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Exothermic Energy Graph
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Endothermic Energy Graph
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Reaction Rates according to Kinetics

• The rate of disappearance of one of the reactant
  or appearance of products

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Rate Influencing Factors

• Nature of the reactants
• Depends on the particular reactant and the bonds
  involved

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Rate Influencing Factors

• Surface Area
• Greater the surface area (smaller pieces) the
  greater the rate
• More exposed the particles, the greater the
  chance of collision

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Rate Influencing Factors

• Temperature
• Increase temp. increase rate (doubled every 10o)
• More collisions due to increase in kinetic energy

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Rate Influencing Factors

• Concentration
• Increase concentration, increase the rate
• More particles therefore a greater chance for
  collision

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Rate Influencing Factors

• Pressure (gases only)
• Greater pressure, greater the rate
• Increase pressure increases the concentration and
  speed of the particles.

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Rate Influencing Factors

• Catalyst
• Substance that increases the rate without being
  permanently changed or used up

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5th way in increase Rxn Rate

• Add a Catalyst

Speeds up a reaction but is not used in the
reaction

• Lowers the activation energy

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Rate Influencing Factors

• Catalyst
• Enzymes are the bodys natural catalyst
• Inhibitors slow the reaction rate such as
  preservatives

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Temperature

• Average kinetic energy of all the particles in
  the sample

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Temperature

• O Kelvin zero energy, absolute zero
• Kelvin Celsius 273
• Celsius Kelvin -273

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Kinetic Theory of Matter

• 1. All matter is composed of small particles

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Kinetic Theory

• 2. Particles of matter are constantly in motion.

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Kinetic Theory

• 3. Collisions between molecules are perfectly
  elastic. This means the total amount of kinetic
  energy is constant.

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Solid, Liquid, Gas Increasing Energy ? ? ? ? ? ?
? ?
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States of Matter

• Fill in chart

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Phase change diagram
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Phase change diagram of water
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Triple point phase diagram
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Triple point phase diagram

• Triple point is the triple point temperature and
  triple point pressure where the three phases
  exist in equilibrium
• Critical point is that at any higher temperature
  and pressure it is no longer possible to
  distinguish between a liquid and a gas. Also
  known as a super-critical fluid

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Heat

• The total amount of kinetic energy and potential
  energy in a substance.
• Heat changes can be measured by changes in the
  temperature of the substance

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Heat

• Cold is the absence of heat.
• Something feels hot as heat flows into you and
  cold as heat flows out.

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Heat

• There are many ways in which heat energy can
  move
• Conduction, Convection and Radiation

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Conduction

• Transfer of heat by direct contact of molecules

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Conduction

• Fast moving molecules collide with the slow
  moving molecules transferring heat energy

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Conduction

• Best in solids
• Examples a spoon left in a hot pot of liquid

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Convection

• Heat transfer in liquids and gases by currents

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Convection

• The hotter, faster molecules are farther apart
  becoming less dense and rise

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Convection

• The cooler, slower molecules are closer together
  becoming more dense and sink

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Convection

• Responsible for air currents, weather phenomena,
  ocean currents, etc.

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Radiation

• Heat transferred through empty space without the
  transfer of matter

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Radiation

• Also called infrared radiation

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Radiation

• Examples sun, fire, stove, heat lamp

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Calculating heat

• Equation
• q cp x m x ?T
• q heat change
• cp specific heat capacity
• m mass
• ?T change in temperature

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Calculating heat

• Example 1 How much heat energy is needed to raise
  the temperature of a 55 g sample of aluminum from
  22.4oC to 94.6oC. the specific heat capacity of
  aluminum is 0.897 J/g oC.

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Calculating heat

• Example 2 During a chemical reaction the
  temperature raises from 21.9oC to 85.3oC. The
  specific heat capacity is 4.18 J/g oC and the
  mass is 100.0 grams. Calculate the heat and
  rewrite the equation including the heat amount,
  H2(g) O2(g) ? H2O(g)

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Pressure

• Three factors that affect the pressure exerted by
  a gas
• The number of gas particles
• The volume of a gas
• Kinetic Energy (Temperature) of the gas particles

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Pressure

• Force of the gas molecules colliding with the
  walls of the container.

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Pressure and the number of molecules are directly
related

• More molecules means more collisions
• Fewer molecules means fewer collisions.
• Gases naturally move from areas of high pressure
  to low pressure because there is empty space to
  move in.

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• If you double the number of molecules

1 atm
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• If you double the number of molecules, you double
  the pressure.

2 atm
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• As you remove molecules from a container

4 atm
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• As you remove molecules from a container the
  pressure decreases

2 atm
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• The pressure will continue to decrease until it
  equalizes with the outside pressure.

1 atm
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Standard Pressure

• Units of Standard Pressure
• 760 mm Hg
• 760 torr
• 1 atm (atmosphere)
• 101,325 Pa (Pascals)
• 101.3 kPa

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Daltons Law of Partial Pressures

• The total pressure exerted by a mixture of gases
  is the sum of the partial pressures of the
  individual pressure oft he individual gases in
  the mixtures.

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Daltons Law of Partial Pressures

• Daltons Law of partial pressures is expressed
  as
• PTOTAL Pa Pb Pc

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• The contents of the first three containers is
  pumped into the fourth container. What is the
  total pressure of the fourth container?

1 atm
2 atm
3 atm
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Gas Collection over Water

• Most gases are collected over water.
• When a gas is collected over water, we must take
  into account the vapor pressure of the water
  molecules exerted. This pressure depends on
  Temperature. (See vapor pressure chart).

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• The gas that is collected is a mixture of the gas
  and water vapor.

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Vapor Pressure Data for Water
Vapor Pressure Data For Water
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Gas Collection over Water

• Example3 A sample of solid potassium chlorate was
  heated in a test tube and decomposed by the
  following reaction
• 2KClO3 ? 2KCl 3O2

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Gas Collection over Water

• The oxygen produced was collected by displacement
  of water at 22C at a total pressure of 754 torr.
  The volume of the gas collected was 0.650 L.
  Find the vapor pressure of water at 22oC.
  Calculate the partial pressure of the dry O2 in
  the gas collected.

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Daltons Law of Partial Pressures

• Example 4 A sample of gas was collected over
  water on a day when the temperature was 24oC and
  the barometric pressure was 706 mm Hg, what was
  the partial pressure of the dry gas?

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Changing the size of the container

• In a smaller container molecules have less room
  to move and hit the sides of the container more
  often
• As volume decreases pressure increases.

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• As the pressure on a gas increases

1 atm
4 Liters
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• As the pressure on a gas increases the volume
  decreases
• Pressure and volume are inversely related

2 atm
2 Liters
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Boyles Law

• In 1662, British chemist Robert Boyle proposed a
  law to describe this behavior of gases.
• Boyles law for a given mass of gas at constant
  temperature, the volume of the gas varies
  inversely with pressure.

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Boyles Law

• We can write Boyles Law as
• P1V1 P2V2
• (at constant temperature)

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Boyles Law

• Examples 5 A sample of gas occupies 10.0 L under
  a pressure of 1 atm. What will its volume be if
  the pressure is increased to 2 atm. Assume the
  temperature is constant.

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Boyles Law

• Examples 6 A sample of oxygen occupies 10.0 L
  under a pressure of 790 torr. At what pressure
  will it occupy 13.4 L if the temperature is
  constant.

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Boyles Law

• Examples 7 A balloon is filled with 30 L of
  helium gas at 1 atm. What is the volume, when
  the balloon rises to an altitude where the
  pressure is only 0.25 atm? (Assume that the
  Temperature does Not change).

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Temperature and Gases

• Raising the temperature of a gas increases the
  volume is the pressure is held constant.
• The molecules hit the walls harder expanding the
  size of the container.

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300 K

• If you start with 1 liter of gas at 1 atm
  pressure and 300 K and heat it to 600 K

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600 K
300 K

• the volume will increase to 2 liters if the
  pressure is constant at 1 atm

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Charles Law

• In 1787, French physicist Jacques Charles
  investigated the effect of temperature on the
  volume of a gas at constant pressure.
• Charles Law the volume of a fixed mass of gas
  is directly proportional to it Kelvin temperature
  if the pressure is kept constant.

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Charles Law

• We can write Charles Law as
• V1 V2
• T1 T2
• Dont forget to change celsius to kelvin

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Charles Law

• Examples 8 A 250 mL sample of gas is confined
  under 1 atm pressure at 25oC. What volume will
  the gas occupy at 50oC if the pressure remains
  constant?

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Charles Law

• Examples 9 A sample of nitrogen gas occupies
  400.0 mL at 100oC. At what temperature in celsius
  will it occupy 200.0 mL if the pressure does not
  change?

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Charles Law

• Examples 10 A balloon, inflated in an
  air-conditioned room at 27C, has a volume of 4.0
  L. It is heated to a temperature of 57C. What
  is the new volume of the balloon if the pressure
  remains constant?

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Temperature and Pressure

• Raising the temperature of a gas increases the
  pressure if the volume is held constant.
• The molecules hit the walls with more force.
• Why is it not a good idea to throw an aerosol can
  into a fire?

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300 K

• If you start with 1 liter of gas at 1 atm
  pressure and 300 K and heat it to 600 K

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600 K
300 K

• the pressure will increase to 2 atm.

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Gay-Lussacs Law

• As the volume of a gas remains constant, the
  pressure is inversely proportional to the
  temperature of the gas.
• A real life example would be the pressure in a
  car tire increases on a hot summer day.

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Gay-Lussacs Law

• Write the law as
• P1 P2
• T1 T2

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Gay-Lussacs Law

• Example 11 A gas has a pressure of 55 mm Hg at
  25oC. What will be the the pressure at 70oC if
  the volume remains constant.

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Gay-Lussacs Law

• Example 12 A gas in a sealed container has a
  pressure of 2.4 atm at 0.0oC. At what temperature
  will the pressure be raised to 5.0 atm?

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Gay-Lussacs Law

• Example 13 The gas left in a used aerosol can is
  at a pressure of 1 atm at 25C (room
  temperature). If this can is thrown into a fire,
  what is the internal pressure of the gas when its
  temperature reaches 927C?

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The Combined Gas Law

• The three gas laws (Charles, Boyle, and
  Gay-Lussac) we have discussed can be combined
  into a single expression called the COMBINED GAS
  LAW

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The Combined Gas Law

• P1V1 P2V2
• T1 T2

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The Combined Gas Law

• Example 14 A sample of oxygen occupies 750 mL at
  room temperature of 21oC on a day when the
  barometric pressure is 745 torr. At what
  temperature will it occupy 700 mL if the pressure
  is decreased to 700 torr?

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The Combined Gas Law

• Example 15 A sample of Neon gas occupies 100.0 L
  at 27.0oCis under a pressure of 1,000.0 torr.
  What volume would it occupy at standard
  conditions?

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The Combined Gas Law

• Example 16 If 6.2 L of a gas at 723 mm of Hg at
  21C is compressed to 2.2 L at 4117 mm Hg, what
  is the temperature of the gas?

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The Ideal Gas Law

• PV nRT
• R 0.0821 L atm/ mol K is called the Universal
  Gas Law Constant.
• P pressure in atm
• V volume in liters
• N number of moles of the gas
• T temperature in kelvin

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The Ideal Gas Law

• It expresses behaviors of gases as they approach
  low pressures and high temperatures. These
  are Ideal gases. Most gases behave ideally
  below 1 atm of pressure. Unless otherwise stated,
  you should always assume you have an ideal gas.
  Ideal gases follow the kinetic theory of gases
  perfectly.

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The Ideal Gas Law

• Example 17 A sample of ammonia gas has a volume
  of 3.5 L at a pressure of 1.68 atm and a
  temperature of O0C. Use the ideal gas law to
  calculate the moles of ammonia present in this
  sample.

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The Ideal Gas Law

• Example 18 What is the volume of 4.04 moles of
  oxygen gas at .954 atm pressure at 25oC?