AP Chemistry - Chapter 10

What are the properties of gases? (5 properties) (CCELF)

• Compressible

• Can diffuse and effuse

• Expand to fill their containers

• Low density

• Fluid - they flow

What are ideal gases?

theoretical gases that perfectly fit all the assumptions of kinetic molecular theory

ideal gas properties (5 properties) (TANCE)

• tiny particles + far apart compared to each other

• average kinetic energy depends on temperature

• no forces of attraction between gas particles

• gas particles are in constant rapid motion (contains kinetic energy)

• elastic collisions (no kinetic energy is lost in collisions)

what is pressure?

the force created by the collisions of molecules with the walls of a container per unit area

Standard Pressure

• 1 atm

• 101.3 kPa

• 760 mmHg/torr

Celsius to Kelvin formula and temperature of absolute zero

C + 273 = K

Absolute zero: -273C/0K

Standard Temperature and Pressure

Temperature: 273K/0C

Pressure: 1 atm | 101.3kPa | 760 mmHg/torr

Gas Laws Formulas

NOTE: Temperature must be in Kelvin and Volume must be in Liters

Relationship between pressure, volume and temperature:

Pressure and Volume are inversely related

Volume and Temperature are proportionally related

Temperature and Pressure are proportionally related

When do real gases behave like an ideal gas?

At higher temperature and lower pressure.

Formula for Density

d=MMP/RT

Value of R Constant

0.08206 L*atm/mol*K

What is the molar volume of a gas at STP?

1mol = 22.4L

How many liters of ammonia can be produced when 12 liters of hydrogen react with an excess of nitrogen? (At STP 1 mole of GASES = 1 liter)

3H₂(g) + N₂(g) → 2NH₃(g)

12L H₂ * (2L NH₃/3L H₂) = 8.0L NH₃

2KClO₃(s) →2KCl(s) + 3O₂(g)

a) How many liters of oxygen gas, at STP, can be collected from the complete decomposition of 50.0 grams of potassium chlorate? (1 mole = 22.4L ONLY AT STP)

b) How many liters of oxygen gas, at 37.0C and 0.930 atmospheres, can be collected from the complete decomposition of 50.0grams of potassium chlorate?

a) 13.7L O₂

b) 16.7L O₂

Dalton’s Law of Partial Pressures

P_total = P_x + P_y + . . .

Mole Fraction Formula

When these valves are opened, what is each partial pressure, the total pressure, and the mole fraction of each gas?

a) Partial Pressure of EACH gas AFTER opening the valves (Use P1V1=P2V2)

b) Total Pressure of Gases AFTER

c) Mole Fraction of Gases AFTER

a) CH₄: 1.20atm | N₂: 0.763atm | O₂: 0.292atm

b) 2.255atm

c) CH₄: 0.532atm | N₂: 0.338atm | O₂: 0.129atm

Fluorine gas is in a 5.0L container that is at 25C and 2 atm. A certain amount of hydrogen gas with a partial pressure of 0.5atm is added to the container. What is the mole ratio of hydrogen gas?

0.2

At a temperature of 560C and a pressure 90 atm, Venus’ atmosphere consist of about 96% CO₂ and 3% N₂, with trace amounts of other gases including water, sulfur dioxide, and sulfuric acid. Calculate the partial pressures of CO₂ and N₂.

CO₂: 86.4 atm

N₂: 27 atm

Kinetic Molecular Theory (5 properties) (VAACE)

• volume of individual particles is around 0

• particles of matter are always in motion

• average kinetic energy is proportional to Kelvin temperature of a gas

• collisions of particles with container walls cause the pressure exerted by gas

• particles exert no forces on each other

What factors effect the kinetic energy of gas particles?

At the same conditions of temperature, all gases have the same average kinetic energy.

Therefore at the same temperature, small molecules move FASTER than large molecules.

Average Kinetic Energy Formula

KE_avg=(3/2)RT

R = 8.314 J/K*mol

Interpret the Maxwell-Boltzmann Distribution Graph

• Average increases as temperature increases

• Spread increases as temperature increases

diffusion

• described spontaneous mixing of gases; the rate of diffusion is the rate of gas mixing

• diffusion is the result of random movement of gas molecules

• rate of diffusion increases with temperature

• small molecules diffuse faster than large molecules

effusion

describes the passage of gas into an evacuated chamber through a small opening

Graham’s Law of Effusion

How much faster does helium, He, diffuse than argon, Ar?

Helium diffuses 3.16 times more faster than argon.