Chapter 1.2 The Ideal Gas Law

Question 1

What does the mass and volume of a mole of a substance depend on?

Answer 1

For solids & liquids, depends on the substance considered

Question 2

What is the molar volume of a gas?

Answer 2

volume occupied by one moe of any gas

Question 3

What Avogadro’s Law?

Answer 3

one mole of any ideal gas always occupies the same volume at a given temperature and pressure regardless of the gas (although different gases have different MOLAR mass)

Question 4

What is STP?

Answer 4

standard temperature and pressure: 273.15ºK (0ºC) and 1 atm (101.325 kPa)

Question 5

How can the ideal gas law be adjusted to determine density and molar mass?

Answer 5

MM = dRT/P

Question 6

What is the relationship between density and pressure?

Answer 6

directly proportional at constant pressure

Question 7

What is the relationship between density and molar mass?

Answer 7

directly proportional at constant pressure and temperature

Question 8

What is Dalton’s Law of Partial Pressures?

Answer 8

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

Question 9

What equation can be used to represent Dalton’s law of Partial Pressures?

Answer 9

Pt = Pa + Pb + Pc + …

Question 10

What is the mole fraction (Xi)?

Answer 10

ratio of number of moles in an individual constituent in a gas mixture over the total number of moles in the mixture; ni/nt

Question 11

How does the mole fraction relate to pressure?

Answer 11

at constant temperature and volume? pressure is directly proportional to moles: Pi/Pt = ni/nt = Xi

Question 12

What must the mole fractions of all gases in a mixture be equal to?

Answer 12

1 = Xa + Xb + Xc

Question 13

What is the relationship between vapour pressure and temperature?

Answer 13

vapour pressure is dependent on temperature

when temperature increases = higher vapour pressure = more evaporation

–> at high altitude = lower pressure = lower vapour pressure = lower boiling point = water boils at less than 100ºC

Question 14

What is boiling point?

Answer 14

temperature at which the vapour pressure of a liquid = atmospheric pressure

Question 15

Why does vapour pressure increase with temperature?

Answer 15

increased temperature = more energy provided to liquid molecules to escape into gas phase

Question 16

What does vapour pressure NOT depend on?

Answer 16

volume of container or presence on another gas

Question 17

What is volatility?

Answer 17

tendency to change to gas state (lower boiling point)

Question 18

How does volatility relate to vapour pressure?

Answer 18

higher volatility = lower boiling point = lower vapour pressure

Question 19

What is the average molar mass of a mixture of different gases?

Answer 19

weighted average of the molar masses of the different gases

Question 20

How is the average molar mass calculated?

Answer 20

MM = XaMMa + XbMMb + Xc*MMc

Question 21

What are the assumptions of the KINETIC MOLECULAR THEORY?

Answer 21

1. the size of molecules is negligible when compared to the space between them and the volume of their container
2. molecules moving through spae are considered to be point particles
3. collisions between particles and the particles and their container are elastic
4. no attractive or repulsive forces between the molecules
5. average kinetic energy of molecules is proportional to temperature in kelvin

Question 22

What is meant by molecules being considered point particles?

Answer 22

molecules do not have vibrational or rotational energy only translational energy

Question 23

What is meant by molecules having elastic collisions?

Answer 23

total momentum and energy of colliding molecules are conserved and molecuels move in straight lines at constant velocities

Question 24

What is the relationship between average kinetic energy of molecules and temperature?

Answer 24

directly proportional
EK = 1/2mu^2

m is mass of 1 molecule and u is speed

Question 25

Why is the mean squared speed used?

Answer 25

not all molecules are moving at the same speed

Question 26

How can you calculated the mean squared speed?

Answer 26

u^2 = [u(a)^2 + u(b)^2 + u(c)^2]/3

Question 27

What are the factors that determine the pressure of a gas in a container?

Answer 27

1. mass (m) of 1 molecule
2. speed (u) averaged of molecules
3. frequency of collisions (#number of collisions per second)

Question 28

What is the pressure equation that relates number of molecules, volume of container, mass of one molecule, and mean square speed?

Answer 28

P = 1/3 N/V * m * u^2

Question 29

What is the relationship between mean squared speed and molar mass?

Answer 29

inversely proportional (light molecule moves faster than heavier molecule if they move at the same speed at the same temperature)

Question 30

What is the unit for root mean squared speed?

Answer 30

meters per second (m s^-1)

Question 31

What is effusion?

Answer 31

flow of gas molecules at low pressure through tiny pores in a container

Question 32

How is the rate of effusion of a gas represented?

Answer 32

rate of effusion = number of moles of gas escaping / time

r(eff) = n(eff)/t

Question 33

What is Graham’s Law?

Answer 33

the rate of effusion of a gas is inversely proportional to the square root of its molar mass
–> (lighter molecules effuse more rapidly that heavier ones)

Question 34

What is the result of lighter molecules effusing faster than heavier ones?

Answer 34

the gas that emerges from a contaniner is ENRICHED in the lighter component

Question 35

What is the enrichment factor (f)?

Answer 35

square root of MMb/MMa