Gas Laws

Gas Pressure

Gas pressure is the result of gas particles colliding with the walls of the container If the volume and temperature of the

container is constant: If gas is added, pressure increases If gas is removed, pressure decreases

Gas Pressure

Gas molecules move from an area of higher pressure to area of lower pressure Opening a can/bottle of soda

Gas Laws Predict the behavior of gases based on

four properties:1. Amount of gas (moles)

2. Pressure

3. Temperature

4. Volume

If one of these properties change, the others change as well.

Boyle’s Law

Irish Chemist Noticed there is an inverse relationship

between the pressure and volume of a gas if the temperature and moles of the gas are

constant If pressure increases, volume decreases If volume increases, pressure decreases

P1V1 = P2V2

Boyle’s Law Continued

P1V1 = P2V2

Practice

1. Air in a container occupies 145.7 mL at 1.08 atm. What volume must the container be to have a pressure of 1.43 atm?

110.04 mL

Practice

1. A balloon filled with He has a volume of 4.0L has a pressure of 210 kPa. If the balloon is compressed to 2.5 L, what will the pressure of He inside the balloon?

Answer: 336 kPa

Practice

1. The volume of a gas at 99.0 kPa is 300 mL. If the pressure is increased to 188 kPa, what is the new volume?

Answer: 157.9 mL

2. The pressure of a sample of He in a 1.00 L container is 0.988 atm. What is the new pressure if the sample is placed in a 2.00 L container?Answer: 0.494 atm

Kelvin Scale and Charles’ Law

Temperature Scales SI scale: degree Celsius (°C) or Kelvin (K) English scale: degree Fahrenheit (°F)

°C + 273 = Temperature in Kelvin Kelvin – 273 = temperature in °C

Kelvin scale is based off the Celsius scale. At 0 K all matter is believed to stop moving

Absolute Zero

Charles’ Law Jacque Charles- French

Physicist

Noticed that the volume of the a gas increased when it is heated, under constant pressure

Direct relationship between temperature and volume

V

T

V

T1

1

2

2

Charles’ Law

Practice

1. A gas sample at 40.0°C occupies 2.32 L. If the temperature is raised to 75°C, what is the volume of the gas if pressure is constant?

Answer: 4.35 L

2. A gas at 89°C occupies 0.67 L. If the volume is increased to 1.12 L, what the temperature be in degree Celsius?

Answer: 148.77 °C

Practice

3. The Celsius temperature of a 300 L sample of gas is lowered from 80.0 °C to 30.0 °C. What will be the resulting volume of this gas?

Answer: 112.5 L

4. What is the volume of the air in a balloon that occupies 0.620 L at 25 °C if the temperature is lowered to 0.00 °C. (convert temps. to Kelvin)

Answer: 0.568 L

Lussac’s Law

Joseph Gay-Lussac explored the relationship between temperature and pressure.

Direct relationship

P

T

P

T1

1

2

2

Practice1. A gas in a sealed container has a pressure

of 123 kPa at 30.0°C. If the pressure is increased to 201 kPa, what is the new temperature?

Answer: 49.02°C

2. The pressure in an automobile tire is 1.88 atm at 25°C. What will be the pressure if the temperature warms to 37°C?

Answer: 2.78 atm

Combined Gas Law Combines Boyle’s, Charles’s, and Lussac’s Laws. Shows the relationship between temperature,

pressure, and volume if the amount of gas is held constant.

P1V1 = P2V2 PV

T

PV

T1 1

1

2 2

2

P

T

P

T1

1

2

2

V

T

V

T1

1

2

2

Pratice

1. A He filled balloon at sea level has a volume of 2.1L at 0.998 atm and 36°C. If it released and rises to an elevation at which the pressure is 0.900 atm and the temperature is 28°C, what will be the new volume of the balloon?

Answer: 1.81L

Practice

2. At 0.00°C and 1.00 atm pressure, a sample of gas occupies 30.0 mL. If the temperature increased to 30.0°C and the entire gas sample is transferred to a 20.0 mL container, what will the gas pressure inside the container?

Answer: 1.66 atm

Ideal Gas Law

The properties of a gas under ideal conditions

PV=nRT

P- pressure (atm or kPa)V- volume (L)n- moles of gas (moles)R- ideal gas constant T- temperature (K)

What is the Ideal Gas Constant? Determined by a series of experiments Relates pressure, volume, temperature, and moles. 2 Ideal Gas Constants

0.0821 8.314

Which one do you use? Based on pressure units

If pressure in atm use 0.0821 If pressure in kPa use 8.314

L atm

mol K

L kPa

mol K

Practice

1. Calculate the number of moles of a gas in a 3.0 L vessel at 300.K with a pressure of 1.50 atm.

PV nRT

n

n moles

( )( . ) ( . )( . )

.

300 30 0 0821 150

018

Practice

1. If the pressure exerted by a gas at 25°C in a volume of 0.044 L is 3.81atm, how many moles of gas are present?

Answer: 0.00685 mol

2. Determine the Celsius temperature of 2.49 moles of gas contained in a 1 L vessel at a pressure of 143 kPa.

Answer: 6.9 K= -266°C

Practice

3. Calculate the volume that a 0.323 mol sample of a gas will occupy at 265 K and a pressure of 0.900 atm.

Answer: 7.8 L

4. What is the pressure in atmospheres of a 0.108 mol sample of He gas at a temperature of 20°C if its volume is 0.505L?

Answer: 5.144 atm

Equations and Information

PV=nRTR= 0.0821 R= 8.314

R= 62.4

L atm

mol K

L kPa

mol K

L mmHg

mol K

PV

T

PV

T1 1

1

2 2

2

P

T

P

T1

1

2

2

V

T

V

T1

1

2

2

P1V1 = P2V2

1 atm = 101.3 kPa1 atm = 760 mmHgConvert All Temperatures To

Kelvin