BEHAVIOR OF GASES

1
BEHAVIOR OF GASES

• Unit 8
• Chemistry
• Langley

Corresponds to Chapter 14 in the Prentice Hall
Chemistry Book
2
PROPERTIES OF GASES

• No definite shape/volume
• Expands to fill its container
• Easily compressed (squeezed into a smaller
  container)
• Compressibility is a measure of how much the
  volume of matter decreases under pressure
• Gases are easily compressed because of the space
  between the particles in a gas

3
PROPERTIES OF A GAS

• Factors Affecting Gas Pressure
• Amount of Gas
• Increase amount, increase pressure
• Volume
• Reduce volume, increase pressure
• Temperature
• Increase temperature, increase pressure
• Relationship between pressure, temperature, and
  volume is explained through the Gas Laws

4
GAS LAWS

• Boyles Law
• Charles Law
• Gay-Lussacs Law
• Combined Gas Law
• Ideal Gas Law
• Daltons Law of Partial Pressure
• Grahams Law

5
BOYLES LAW

• If the temperature is constant, as the pressure
  of a gas increases, the volume decreases
• For a given mass of gas at constant temperature,
  the volume of a gas varies inversely with
  pressure
• As volume goes up, pressure goes down
• As volume goes down, pressure goes up
• P1V1 P2V2

6
BOYLES LAW

• Real Life Example
• As you push on the end of a syringe, the volume
  inside the syringe decreases as the pressure on
  the syringe increases
• Mathematical Example 1
• P1 758 torr V1 5.0L P2 ? V2 3.5L

7
BOYLES LAW

• Mathematical Example 2
• If 4.41 dm3 of nitrogen gas are collected at a
  pressure of 94.2 kPa, what will the volume be for
  this gas at standard pressure if the temperature
  does not change?

8
CHARLES LAW

• As the temperature of an enclosed gas increases,
  the volume increases, if the pressure is constant
• The volume of a fixed mass of gas is directly
  proportional to its Kelvin temperature if the
  pressure is kept constant
• As volume goes up/down, temperature goes up/down
• V1 V2 Temperature must be in Kelvin!
  T1 T2

9
CHARLES LAW

• Real Life Example
• Balloon Lab-As the temperature of the water is
  increased, the volume of the balloon is
  increased.
• Coke Can-Fill a coke can with a small amount of
  water, as you heat the water inside to near
  boiling, immediately invert the coke can into
  ice-cold water so the coke can is experiencing a
  dramatic drop in temperature, volume of can will
  decrease (can will crush in on itself)

10
CHARLES LAW

• Mathematical Example 1
• V1 250mL T1 300K V2
  321mL T2 ?
• Mathematical Example 2
• With a constant pressure, the volume of a gas is
  increased from 15.0L to 32.0L. If the new
  temperature is 20.0C, what was the original
  temperature?

11
GAY-LUSSACS LAW

• As the temperature of an enclosed gas increases,
  the pressure increases, if the volume is constant
• The pressure of a gas is directly proportional to
  the Kelvin temperature if the volume remains
  constant
• P1 P2 Temperature must be in Kelvin!
  T1 T2

12
GAY-LUSSACS LAW

• Real Life Example
• Tires
• The faster a car goes, the higher the temperature
  of the tire gets and the higher the pressure
  inside the tires
• Mathematical Example 1
• P1 ? T1 456K P2 789mmHg T2 326K

13
GAY-LUSSACS LAW

• Mathematical Example 2
• The pressure in a tire is 1.8 atm at 20C. After
  a 200 mile trip, the pressure reading for the
  tire is 1.9 atm. What is the temperature inside
  the tire at that new pressure?

14
COMBINED GAS LAW

• Combines Boyles, Charles, and Gay-Lussacs laws
• Describes the relationship among temperature,
  pressure, and volume of an enclosed gas
• Allows you to perform calculation for situations
  IF and ONLY IF the amount of gas is constant
• P1V1 P2V2
  Temperature must be in
  Kelvin!
• T1 T2

15
IDEAL GAS LAW

• When you need to account for the number of moles
  of gas in addition to pressure, temperature, and
  volume, you will use the Ideal Gas Equation
• Modified version of the Combined Gas Law
• PV nRT
• n number of moles
• R ideal gas constant
• 0.08206 (L-atm/mol-K)
• 62.4 (L-mmHg/mol-K)
• 8.314 (L-kPa/mol-K)

16
IDEAL GAS LAW

• Mathematical Example 1
• What is the pressure in atm exerted by 0.5 moles
  of N2 in a 10L container at 298 Kelvin?
• Mathematical Example 2
• What is the volume in liters of 0.250 moles of O2
  at 20C and 0.974 atm?

17
IDEAL GAS LAW

• Mathematical Example 3
• What is the temperature of 76 grams of Cl2 in a
  24L container at 890mmHg?
• Mathematical Example 4
• A deep underground cavern contains 2.24x106L of
  CH4 at a pressure of 1.50x103kPa and a
  temperature of 315K. How many kilograms of CH4
  does the cavern contain?

18
IDEAL vs. REAL GASES

• Ideal gases follow the gas laws at all conditions
  of pressure and temperature
• Conforms exactly to the all the assumptions of
  the kinetic theory (no volume, no particle
  attraction)?doesnt exist
• Real gases differ mostly from an ideal gas at low
  temperature and high pressure
• Under other conditions, behave as an ideal gas
  would

19
DALTONS LAW

• In a mixture of gases, the total pressure is the
  sum of the partial pressure of the gases
• Partial pressure is the contribution each gas in
  a mixture makes to the total pressure
• At constant volume and temperature, the total
  pressure exerted by a mixture of gases is equal
  to the sum of the partial pressures of the
  component of gases
• Ptotal P1 P2 P3

20
DALTONS LAW

• Mathematical Example 1
• In a container there are 4 gases with the
  following pressures Gas 1-2.5 atm, Gas 2-1.9
  atm, Gas 3-798 mmHg, Gas 4-2.1 atm find the
  total pressure in the container.

21
DALTONS LAW

• Mathematical Example 2
• In a sample of HCl gas, the pressure of the gas
  is found to be 0.87 atm. If hydrogen makes up
  34 of the gas, what is the pressure of the
  hydrogen?

22
GRAHAMS LAW

• The ratio of the speeds of two gases at the same
  temperature is equal to the square root of the
  inverted molar masses
• The relative rate of diffusion
• Diffusion is the tendency of molecules to move
  toward areas of lower concentration to areas of
  higher concentration until the concentration is
  uniform throughout
• Gases of lower molar mass diffuse and effuse
  faster than gases of higher molar mass
• Effusion is when gas particles escape through
  tiny holes in a container

23
GRAHAMS LAW

• v(Molar MassB/Molar MassA)
• The rates of effusion of two gases are inversely
  proportional to the square roots of their molar
  masses
• Use periodic table to get molar masses

24
GRAHAMS LAW

• Mathematical Example 1
• What is the ratio of the speeds of Helium
  compared to Oxygen?
• Mathematical Example 2
• If Co2 has a speed of 22 m/s at 20C, what is the
  speed of HCl at the same temperature?