Gas!!!

1
Gas!!!

• Its Everywhere!!!!

2
Kinetic Molecular Theory

• Most of the volume occupied by a gas is empty
  space
• Collisions between gas particles are elastic
  collisions
• Energy is transferred between the particles

3
Kinetic Molecular Theory

• Gas particles are in constant motion
• Possess kinetic energy (energy of motion)
• Kinetic Energy in a gas depends on the
  temperature
• KE ½ mv2

4
Kinetic Molecular Theory

• Expansion
• No definite shape or volume
• Fluidity
• Gases flow like liquids
• Low Density
• Most of the volume is empty space
• Compressibility
• Since mostly empty space, particles can be
  squeezed into a smaller volume

5
Diffusion

• Spontaneous mixing of gas particles caused by
  their random motion

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Effusion

• A process by which gas particles pass through a
  small opening

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Diffusion vs. Effusion
8
Real vs. Ideal

• Ideal Gas An imaginary gas that perfectly fits
  all of the assumptions of the Kinetic Molecular
  Theory
• Real Gas A gas that does not behave completely
  according to the assumptions of the Kinetic
  Molecular Theory
• A real gas can behave like an ideal gas under
  high temperature and low pressure conditions

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STP

• STP Standard Temperature and Pressure
• Standard Temperature 0C
• Standard Pressure 1 atm

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Pressure

• The force per unit area on a surface
• Barometer a device used to measure atmospheric
  pressure

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Units of Pressure

• Millimeters of mercury mmHg
• Torr
• Atmosphere atm
• Pascal Pa
• Kilopascal - kPa

12
Important Conversion

• 1 atm 760 mmHg
• 1 atm 760 torr
• 1 atm 101.325 kPa

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Temperature

• Kelvin is the standard temperature scale used
  when dealing with gases
• Absolute zero 0 K
• Unreachable!
• Temperature in Kelvin Temperature in Celsius
  273
• Temperature in Celsius Temperature in Kelvin
  273
• 0C 273 K
• 25C 298 K (Room Temp)
• 0 K -273C (Absolute Zero)

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Boyles Law

• The volume of a gas at constant temperature
  varies indirectly with pressure.

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Example

• The pressure exerted on a 240 mL sample of
  hydrogen gas at constant temperature is increased
  from 0.428 atm to 0.724 atm. What will the final
  volume of the sample be?

• V1 240.0 mL
• V2 ?
• P1 0.428 atm
• P2 0.724 atm

P1V1 P2V2
(0.428 atm)(240.0 mL) (0.724 atm)V2
V2 142 mL
16
Charles Law

• The volume of a gas at constant pressure varies
  directly with the temperature

17
Example

• A sample of air has a volume of 140.0 mL at 67C.
  At what temperature will its volume be 50.0 mL at
  constant pressure?

• V1 140.0 mL
• V2 50.0 mL
• T1 67C 273 340 K
• T2 ?

V1
V2
V2
T1
(50.0 mL)(340K)
T2


121 K

140.0 mL
T1
T2
V1
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Gay-Lussacs Law

• The pressure of a gas at constant volume varies
  directly with the temperature

19
Combined Gas Law
20
Example

• A helium filled balloon has a volume of 50.0 L at
  25C and 1.08 atm. What volume will it have at
  0.855 atm and 10C?

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Solution
Step 1 List what you are given.

• V1 50.0 L
• V2 ????
• P1 1.08 atm
• P2 0.855 atm
• T1 25C 273 298 K
• T2 10C 273 283 K

Must Convert to Kelvin!!!!
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Solution

• Step 2 Solve the Combined Gas Law for your
  unknown.

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Solution

• Step 3 Solve!

(1.08 atm)(50.0 L)(283 K)
V2
(0.855 atm)(298 K)
V2
60.0 L He
24
Daltons Law

• The total pressure of a mixture of gases is equal
  to the sum of the partial pressures of the
  component gases.

PT P1 P2 ..... Pn
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Example

• What is the total pressure of a gas containing a
  mixture of three gases whose partial pressures
  are 20 kPa, 10 kPa, and 30 kPa?

PT P1 P2 ..... Pn
PT 20 kPa 10 kPa 30 kPa
PT 60 kPa
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Ideal Gas Law

• The mathematical relationship among pressure,
  volume, temperature, and the number of moles of a
  gas.

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Example

• Calculate the volume, in liters, occupied by 2.00
  mol of H2 at 300 K and 1.25 atm. (R
  0.0821)

PV nRT
nRT
V
P
(2.00mol)(0.0821)(300K)
V
1.25 atm
V 39.4 L
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Avogadros Law

• Equal volumes of gases at the same temperature
  and pressure contain equal numbers of molecules.

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Gas Stoichiometry
How many liters of oxygen are required to produce
2 L of carbon dioxide?

• 2CO O2 2CO2

2L CO2
1L O2
1L O2
2L CO2