CH. 1.2 - THE IDEAL GAS LAW

Question 1

Explain Dalton’s Law of Partial Pressures: Pₜ = P₁ + P₂ + P₃

Answer 1

The total pressure exerted by a mixture of gases is the sum of all the partial pressures of these gases.

Question 2

The sum of all mole fractions should equal…

Answer 2

1

Question 3

In a container filled with different gases, how will the gases behave?

Answer 3

Each gas will maintain its own behaviors and behave as its alone in this container

Question 4

What is the concept behind the molar volume of gas?

Answer 4

At a standard temperature and pressure, any gas will take up the same amount of space (have the same volume)

Question 5

At STP, what is the volume of space 1 mole of gas will take up

Answer 5

22.4L

Question 6

What are the two ways/equations we can use to find the mole fractions of a mixture?

Answer 6

1. Xᵢ = nᵢ/nₜ
2. Xᵢ = Pᵢ/Pₜ
   we can use moles or pressure to find the mole fractions

Question 7

Why can we use moles or pressure to find the mole fractions of a gas mixture?

Answer 7

because moles and pressure are directly related at a constant temperature and volume

Question 8

At equilibrium, the rates of evaporation and condensation will be the same, meaning the pressure of H20 (g) will… _________

Answer 8

remain constant

Question 9

When is equilibrium reached with water vapor?

Answer 9

when the rate of evaporation = the rate of condensation

Question 10

What happens when equilibrium is reached with water vapor?

Answer 10

the amount of water vapor in the air stays constant and so does the vapor pressure

Question 11

What equation do you use to find the total pressure of the gas in the flask when dealing with water vapor?

Answer 11

Pₜ = Pₐᵢᵣ + Pᵥᵥₐₜₑᵣ ᵥₐₚₒᵣ

where Pₐᵢᵣ = pressure exerted by the air,
and Pᵥᵥₐₜₑᵣ ᵥₐₚₒᵣ = pressure from the water vapor

Question 12

What does the vapor pressure of any liquid depend on?

Answer 12

temperature

Question 13

When temperature INCREASES, what happens to the vapor pressure?

Answer 13

the molecules in the liquid have more energy and be more likely to evaporate, which will INCREASE the vapor pressure

Question 14

Why do volatile liquids have higher vapor pressures at a given temperature?

Answer 14

They have lower boiling points and evaporate easily, meaning that they need less energy to change states.

Question 15

How do you find the average molar mass of a mixture?

Answer 15

MM = (Xₐ* MMₐ) + (Xb* MMb) + (X꜀* MM꜀)

where X is the mole fraction of the specific gas and MM is the molar mass of that specific gas

Question 16

What are 4 assumptions about the Kinetic Molecular Theory of Gases?

Answer 16

1. They have negligible molecular size
2. They are point particles with only translational kinetic energy
3. They have elastic collisions and constant velocity
4. They don’t have any intermolecular forces

Question 17

Explain why gases have negligible molecular size according to the Kinetic Molecular Theory of Gases.

Answer 17

• the actual size of a gas molecule is so small that it can be ignored when considering the overall volume of the gas

Question 18

Explain why gases are point particles with translational energy according to the Kinetic Molecular Theory of Gases.

Answer 18

• they get their energy purely from motion through space, with no internal vibrational or rotational energies

Question 19

Explain why gases have elastic collisions and constant velocity according to the Kinetic Molecular Theory of Gases

Answer 19

• there is no net loss of kinetic energy during collisions, meaning molecules will rebound without changing their speed

Question 20

Explain why gases don’t have any intermolecular forces according to the Kinetic Molecular Theory of Gases

Answer 20

• gases do NOT exert attractive or repulsive forces on one another meaning they will move independently until they collide

Question 21

How is the temperature and average kinetic energy related?

Answer 21

average kinetic energy and temperature are proportional to eachother
- when temperature increases, so does the average kinetic energy

Question 22

TRUE OR FALSE: all gas molecules move at the same speed

Answer 22

FALSE: there is a distribution of speeds where some molecules move faster and others slower

Question 23

What 3 factors influence gas pressure?

Answer 23

1. The mass of each molecule
2. The speed of each molecule
3. The frequency of collisions

Question 24

How does the mass of a molecule influence gas pressure?

Answer 24

heavier molecules contribute more to pressure because each collision will increase momentum

Question 25

How does the speed of a molecule influence gas pressure?

Answer 25

faster moving molecules collide more frequently and with greater force, therefore increasing pressure

Question 26

How do the frequency of collisions affect gas pressure?

Answer 26

the # of molecules and the volume of the container determine how often molecules collide with each other and the container walls.

MORE molecules and/or a SMALL volume with increase collisions and pressure.

Question 27

What equation relates pressure to molecular properties?

Answer 27

P = 1/3 (N/V) (m)(u^2)

where p = pressure
N = # of molecules
V = volume of container
m = mass of one molecule
u^2 = mean-square speed

Question 28

What is the Root-Mean-Sqaure (RMS) Speed?

Answer 28

the measure of the average speed of gas molecules

Question 29

TRUE OR FALSE: lighter gases move FASTER than heavier ones at the same temperature

Answer 29

TRUE: because the RMS speed of 2 different gases is INVERSELY proportional to the square root of their molar masses

Question 30

What is effusion?

Answer 30

the process at which gas molecules pass through a tiny opening from a region of high pressure to low pressure

Question 31

TRUE OR FALSE: effusion typically occurs at low pressures

Answer 31

TRUE

Question 32

What 3 factors affect effusion

Answer 32

1. Molecular Mass
2. Temperature
3. Size of Pore/Hole

Question 33

How does molecular mass affect effusion?

Answer 33

lighter molecules have faster effusion rates than heavier ones because they move faster at a set temperature

Question 34

How does temperature affect effusion?

Answer 34

higher temperatures increase molecular speeds, therefore also increasing effusion rates

Question 35

How does the size of pore/hole affect effusion?

Answer 35

smaller pores restrict larger molecules more effectively, increasing the rate of effusion

Question 36

What is Graham’s Law?

Answer 36

states that the rate of effusion is inversely proportional to the square root of its molar mass

Question 37

What is an enrichment factor?

Answer 37

ratio that compares how much one gas effuses vs the other based on their molar masses