Chemistry - Unit 10 Gas Laws

Kinetic Molecular Theory

It's the theory that states molecules are in constant motion, and their speed changes with temperature.

STP Values

Standard Temperature and Pressure (STP) is 273K (0°C) and 1 atm.

Kelvin Scale

It's the temperature scale where 0K is absolute zero.

Convert 120°C to Kelvin

120 + 273 = 393K

Convert 353K to Celsius

353 - 273 = 80°C

Random Molecular Motion

Is greatest in the gas phase.

Boyle’s Law

As pressure increases, volume decreases (inverse relationship).

Charles’s Law

As temperature decreases, volume decreases (direct relationship).

Gay-Lussac’s Law

As temperature increases, pressure increases (direct relationship).

Balloon in Freezer

Will shrink because the volume decreases as temperature decreases.

Cylinder with Oxygen at 7.00 atm & 150K; temperature increases to 300K

Use the gas law to calculate new pressure.

The pressure and temperature of 2.50L gas are doubled; initial conditions are 3.00 atm and 300K

Final volume must be calculated using gas law equations.

500.0 mL gas at 800 mm Hg decreases to 250.0 mL

Use Boyle’s Law to determine new pressure.

3.0L of gas raised from 10°C to 100°C

Calculate the new volume using Charles’s Law.

Propane Tank

55L tank has 3.0 moles of gas; if half is used, 1.5 moles remain.

Gas Volume at 30.0L, 40°C, 2.00 atm

Calculate how many moles of gas it holds.

Gas at 45 mm Hg and 100K warms to 27°C

Determine new pressure using Gay-Lussac’s Law.

Mixture of Gases

Helium = 6.5 atm, Neon = 12.4 atm; total pressure = 6.5 + 12.4.

35 mol O2 and 65 mol H2

Total pressure = 7.4 atm; determine partial pressures.

2.50 mol gas at 4.50L, STP

Calculate volume at 2.25L.

Relationship: Pressure & Volume

Inversely proportional (Boyle's Law).

Relationship: Volume & Temperature

Directly proportional (Charles's Law).

Relationship: Pressure & Temperature

Directly proportional (Gay-Lussac's Law).

Relationship: Moles & Volume

Directly proportional (Avogadro’s Law).

7.00 atm Oxygen at 150K, temp increases to 300K

Use gas law to find new pressure.

A gas container initially at 45 mm Hg, 100K, warms to 27°C

Calculate new pressure.

What is compressibility?

It's the ability of a gas to be compressed due to space between molecules.

A 40.0-mL soap bubble at 1 atm, pressure changes to 0.95 atm

Calculate new volume.

Gas sample pressure decreases from 1.0 atm to 0.5 atm, new volume 20L

Find the original volume.

120L of gas at 2.3 atm, 340K

Calculate number of moles using the Ideal Gas Law.

Gas Law Pressure Units

Atmospheres (atm), kilopascals (kPa), millimeters of mercury (mmHg), torr.

Gases are defined by

They are compressible, flow freely, and do not have a defined volume or shape.

If temperature decreases, pressure

Also decreases, since gas molecules slow down.

Gas Pressure

Is caused by molecules colliding with each other and container walls.

Gas Law Volume Units

Liters (L).

Dalton’s Law of Partial Pressures

The total pressure of a mixture is the sum of the individual pressures.

0 Kelvin is absolute zero because

There is no movement of particles.

Gas Law Temperature Scale

Always use Kelvin for gas law calculations.

STP Conditions

273 Kelvin and 1 atm.

STP Stands for

Standard Temperature and Pressure.

What happens to molecules when temperature increases?

They move faster and pressure increases.

Kinetic Energy & Gas Law

Is related to temperature.

Convert Celsius to Kelvin

Add 273 to the Celsius temperature.

Balloon placed in freezer

Volume decreases due to lower temperature.

Which phase has the greatest molecular motion?

Gas phase.

Negative Kelvin temperature

Not possible, because absolute zero is the lowest theoretical temperature.

Convert 200K to °C

200 - 273 = -73°C

Convert -173°C to K

-173 + 273 = 100K

Convert 300K to °C

300 - 273 = 27°C

Convert 25°C to K

25 + 273 = 298K

Three gases (N2, Xe & C2H4) have pressures of 0.50 atm, 0.75 atm, and 0.95 atm

Total pressure = 0.50 + 0.75 + 0.95 = 2.16 atm.

A gas is 5.00L at 1.08 atm, what is the pressure at 10.0L?

Use Boyle’s Law to calculate.

Temperature is a measure of

Average kinetic energy.

A tire at 260K has a pressure of 1.50 atm, what is the pressure at 288K?

Use Gay-Lussac's Law to calculate.

If a balloon has a volume of 45.0L at 298K and is heated to 328K

Find the new volume using Charles’s Law.

A sample of hydrogen gas is 25L at 5 atm, what is the pressure if the volume is 5L?

Use Boyle’s Law to solve.

A balloon has a volume of 1.2L at 298K, what is the volume at 258K?

Use Charles's Law to find the new volume.

A soap bubble is 40.0mL at 1 atm, what is the volume at 0.95 atm?

Use Boyle’s Law.

What is the pressure on a gas sample that decreases from 1.0 atm to 0.5 atm if the new volume is 20L?

Use Boyle’s Law.

How many moles occupy 120L at 2.3 atm and 340K?

Use the Ideal Gas Law.

What are the units of pressure?

atm, kPa, mmHg, torr.

What happens if temperature decreases?

Pressure decreases due to lower kinetic energy.

What happens to molecules as temperature increases?

Speed and pressure increase.

According to Kinetic Molecular Theory, kinetic energy is related to

Temperature.

What happens to a balloon when placed in a freezer?

Volume decreases.

The random molecular motion of a substance is greatest in the

Gas phase.

Can you have negative Kelvin temperatures?

No, because absolute zero is the lowest possible temperature.