GAS LAWS

Chapter 14 in Prentice Hall Chemistry

How are each of the following related?

1) Pressure and Temperature

2) Pressure and Volume

4) Temperature and Volume

3) Pressure and Amount of Gas

*Consider all other variables constant. Come up with an example which confirms your hypothesis.

5) Volume and Amount of Gas

BELLWORK

Factors Affecting Pressure

Amount of Gas: Increasing the number of particles increases collisions, which increases pressure. Removing particles reduces pressure.

Volume: Increasing the volume will decrease the pressure of a gas since collisions are less likely. Decreasing the volume has the opposite effect.

Temperature: Increasing the temperature increases the speed of the molecules, which leads to more collisions and greater pressure.

Decreasing the temperature has the opposite effect.

David Bowie

Units of Pressure

1 atm = 101.325 kPa = 760 torr = 760 mmHg = 14.7 psi

atm = atmosphereskPa = kilopascals

torr = torrmmHg = millimeters of mercury

psi = pounds per square inch

Units can easily be converted from one to another by using dimensional analysis.

Example: 0.89 atm = 760 torr = 676.4 torr1 atm

Boyle’s LawIf the temperature is constant, as pressure of a gas increases the volume decreases.

PV = K P1V1 = P2V2

Example: A ballon contains 30.0 L of helium gas at 103 kPa. What is the volume of the

helium when the balloon rises to an altitude where the pressure is only 25.0 kPa, assuming

constant temperature?

Year: 1662

Charles’s LawIf the pressure is constant, as temperature of a

gas increases the volume increases. *Temperature must be in Kelvin for all gas laws*

V= K V1 = V2

T T2T1

Year: 1787Example: A balloon inflated in a room at 240C

has a volume of 4.00L. The balloon is then heated to a temperature of 580C. What is

the new volume if the pressure remains constant?

*To get from 0C to K, add 273

Gay-Lussac’s LawAs the temperature of an enclosed gas increases,

the pressure increases at constant volume.

P= K P1 = P2

T T2T1

Year: 1802

Example: The gas in a used aerosol can is at a pressure of 103 kPa at 250C. If the can is

thrown onto a fire, what will the pressure be when the temperature reaches 9280C?

*To get from 0C to K, add 273

Combined Gas Law

The combined gas law allows you to do calculations for situations in which only the

amount of gas is constant.

Example: The volume of a gas filled balloon is 30.0 L at 313 K and 153 kPa. What would the

volume be at STP?

PV= K P1V1 = P2V2

T T2T1

Freddie Mercury

Ideal Gas Law PV = nRT

The moles of gas is no longer a constant, and is now represented by “n”. There is also a gas constant, “R”. The gas constant depends on the unit for pressure.

R = 0.0821 L*atmmol*K

R = 8.31 L*kPamol*K

Example: A deep underground cavern contains 2.24 x 106 L of CH4 gas at a pressure of 1.50 x 103 kPa and a

temperature of 420C. How many moles of CH4 gas does the cavern contain?

Ideal vs. Real GasesIn order to behave as an ideal gas, gases could not have any volume and could be

attracted to other gas molecules.

This is impossible, however, under certain conditions real gases can behave very similarly to an ideal gas.

Real gases differ most from an ideal gas at low temperatures and high pressures.

Checkpoint: Why are real and ideal gases different under these conditions?

Dalton’s Law of Partial PressureIn a mixture of gases, the total pressure is

the sum of the partial pressures of the gases at constant temperature.

Ptotal= P1 + P2 + P3 + ...

Example: Air contains O2, N2, CO2, and trace amounts of other gases. What is the partial pressure of O2 at 101.30 kPa of total pressure if the partial pressures of N2, CO2, and other gases is

79.10 kPa, 0.040 kPa, and 0.94 kPa, respectively?

Graham’s Law of effusion

Year: 1840

Diffusion: The tendency of molecules to move toward areas of lower concentration until the

concentration is uniform throughout.

Effusion: A gas escapes through a tiny hole in a container

Gases of lower molar mass diffuse and effuse faster than gasses of higher molar mass.

There are equations which describe this phenomena, but we will not cover them in this class.

CrashCourse Chemistry: Ideal Gas Law

http://www.youtube.com/watch?v=BxUS1K7xu30&list=PL8dPuuaLjXtPHzzYuWy6fYEaX9mQQ8oGr