Gen Chem Class 3

Question 1

T/F: a physical change affects only intermolecular forces but no intramolecular forces

Answer 1

true

Question 2

T/F: all molecules experiencce intermolecular attraction

Answer 2

True, at least dispersion forces

Question 3

the average kinetic energy of the molecules of a substance direcly affect its _________

Answer 3

phase (aka state)

the phases are solid, liquid, or gas

Question 4

the higher the average kinetic energy of a substance, the ____\_higher/lower___ its entropy

Answer 4

higher

Question 5

phase transitions occur most directly as a result of change in ______

Answer 5

temperature,

because temperature can break and form intermolecular interactions

Question 6

what are the 3 phases in order from lowest to highest kinetic energy

Answer 6

solid, liquid, gas

Question 7

T/F when enough energy (from heat) is absorbed for molecules to move around freely around one another, the solid becomes a liquid

Answer 7

true

the molecules in liquid state still make contact with one another but they have enough energy to escape fixed positions

Question 8

T/F: all gases are free of intermolecular forces

Answer 8

false, only ideal gases

Question 9

T/F: molecules in the gas phase move freely from one another and experience very little if any intermolecular interactions

Answer 9

true

Question 10

in phase change, “fusion” secribes what process?

Answer 10

melting

Question 11

T/F: phase changes that bring molecules closer together release heat and visa versa

Answer 11

true

changes that bring molecules closer together are: condensation, freezing, deposition*

changes that spread molecules farther apart: melting/fusion, vaporization, sublimation**

^{<em>*deposition=transition from gas to solid phase</em>}

^{<em>** sublimation=transition from solid to gas phase</em>}

Question 13

specific heat capacity

Answer 13

the amount of heat required to raise the temperature of 1 mass unit of substance by 1 degree celcius

Question 14

density of ice >/< ? density of water

Answer 14

density of ice<density>
</density>

Question 15

what does the phase diagram for water look like and why?

Answer 15

slope is negative because H20 is a special liquid. Its solid form actually is lower pressure than its liquid form and adding pressure will turn it into a liquid

Question 16

how do you identify the mp and bp on a phase diagram

Answer 16

it’s the intersection of the horizonal line representing 1 atm with the lines representing barriers between phases

Question 17

what equation do we use to find:

1. ^{specific heat}
2. ^{temperature change for a reaction}
3. ^{mass of a sample undergoing phase change}
4. ^{heat added or released by substance}

Answer 17

1. ^{c= specific heat (in cal/g·°C)}
2. ^{ΔT = temperature change (in cal/g or kJ/mol)}
3. ^{m=mass of sample (in g or moles)}
4. ^{q=heat added or released (in cal or kcal)}

q=mcΔT

Question 18

the fact that water typically has a higher specific heat than other substances is because of

Answer 18

The breaking and reforming of hydrogen bonds in liquid water can absorb a large amount of heat, making water resistant to temperature change.

*specific heat of water is 1 cal

Question 19

how do you find the amount of heat absorbed or released by a phase change?

Answer 19

q=nΔH_{fusion or vaporization}

_{where n=amount of the substance in moles or grams depending on the terms used for ΔH.. they cancel out)}

_{q=mount of heat absorbed or released by a phase change. in cal.}

Question 20

T/F: when a substance absorbs or releases heat, either its temperature changes or it will undergo a phase change but no both at the same time

Answer 20

true

this is represented by the heating curve

Question 21

T/F: the specific heat of a substance is the same no matter what phase its in

Answer 21

FALSE: it depends on phase e..g. the sp. heat of liquid water is different from that of ice

Question 22

1 cal is #? Joules?

Answer 22

1 cal = 4.2 J

Question 23

ΔT is inversely proportional to ______

Answer 23

specific heat

_{from rearranging q=mcΔT}

Question 24

molecules with strong intermolecular forces tend to have higher/lower specific heats

Answer 24

higher

Question 25

How do you solve this problem and why do you solve it that way?

Answer 25

when calculating the total energy required to go from one phase to another where the temperature changes, you have to add the product of each of the phase change equations (q=nΔH + q=mcΔT)

you solve it this way because a substance independently changes because of temperature and because of phase change but not at the same time so they have to be added.

Question 26

ideal gas law

Answer 26

PV=nRT

^{P=pressure of the contained gas in atm}

^{V=volume of container _{*see below}}

^{n= number of moles of substance (22.4 of ideal gas under STP)}

^{R= universal gas constant, 0.08 L-atm/K-mol _{because the constant is in L, you must convert all volumes into L}}

^{T=temperature of system in Kelvin}

Question 27

T (in K) =?

Answer 27

T (in °C) + 273

Question 28

How do you solve this problem?

Argon at pressure of 2 atm, fills a 0.1 L vial at a temp of 0°C. what would the pressure of the argon be if we increase the volume to 0.5L, and the temperature is 100°C.

Answer 28

Since it’s asking about a change and 2 terms in the equation are constant throughout the change and also not given in the problem, we can relate the before and after with a proportionality equation:

P₁V₁/T₁ = P₂V₂/T₂

then solve for P₂

Question 29

1 atm = #? torr = #? Hg ~ #? kPa

Answer 29

1 atm = 760 torr = 760 Hg ~ 100kPa

Question 30

average kinetic energy of the molecules of an ideal gas is directly proportional to the absolute temperature of a sample

what does this look like in equation form?

Answer 30

KE_avg ∝T

Question 31

T/F: total kinetic energy of gas in a container is the same after each molecule collision as before

Answer 31

true

Question 32

T/F: If two equal-volume containers hold gas at the same pressure and temperature, then they contain the same number of particles regardless of the identity of the gas

Answer 32

true

(avogadro’s law)

Question 33

R (from equation for pressure)= #?

Answer 33

0.08

a constant

Question 34

T/F: the average kinetic energies of 2 gases are not equal if the mixture is of real and ideal gases

Answer 34

FALSE: they are still equal as long as the gases are at the same temperature

Question 35

what are the conditions that maintain ideality (i.e. make real gases act more ideal)

Answer 35

high temperature

low pressure

*conversely, real gases deviate most from ideal behavior under conditions of high pressure and low temperature.

mnemonic: gases can’t be their ideal selves when they are under high pressure.

Question 36

the more ideal the gas the greater/weaker the intermolecular force

Answer 36

weaker

Question 37

the molecule with the greatest number of atoms (polyatomic molecule) will take up more volume. This means that it is more/less ideal (ideal gas).

Answer 37

less

a molecule with one atom will take up less volume and will be most ideal, which is how the ideal gases get their name (they are gases in their atomic state)

in contrast from O₂ for example which is only a gas when it’s polyatomic

Question 38

T/F: H-F can take part in hydrogen bonding

Answer 38

true, but flourine is the only halogen that can do so

Question 39

Dalton’s law

Answer 39

P_tot = p_A + p_B + p_C

_{ie the sum of the pressure is equal to the sum of each of the pressures of the individual gases}

Question 40

partial pressure of a gas is equal to

Answer 40

its mole fraction times the total pressure

*mole fraction=fancy way of saying the ratio of particles of that gas to the total number of particles of the mixture

total pressure= in atm

Question 41

effusion refers to

Answer 41

the escape of a gas molecule througha tiny hole comparable in size to the particle size

Question 42

for two gases in the same container (kinetic energy of gases is equal), the gas with the heavier molecule will have slower/faster velocity

Answer 42

slower

Question 43

for two gases in the same container (kinetic energy of gases is equal), how can we compare the relative velocities of each gas?

Answer 43

by using KE=1/2mv² and then setting their KE equal:

1/2m₁v²₁ = 1/2m₂v²₂

→ v²₂/v²₁ = m₁/m₂

→ √ v²₂/v²₁ = √m₁/m₂

→ v₂/v₁ = √m₁/m₂

_{this gives us the ration of velocities between the gases i.g. Graham’s Law of Effusion}

Question 44

Graham’s Law of Effusion

Answer 44

(taken from setting KE₁ = KE₂ )

v₂/v₁ = √m₁/m₂

Question 45

T/F: the molecules of 2 different gases at the same temperature in the same compartment have the same average kinetic energy

Answer 45

True

Question 46

ideal gases take up no molecular volume

Answer 46

true

real gases do have volume, so if you have a mix of ideal and real gas, the total volume available to the gases is less than the total volume of the flask, whereas if it were ideal gas, the total volume available to the gas is equal to the volume of the flask.

Question 47

what is the relationship between ideality, mass and intermolecular forces?

Answer 47

↑ideal ↓m ↓IMF

Question 48

T/F: partial pressure is determined by the number of moles of a gas and is not affected by the mass of the molecules.

Answer 48

true, so in this picturem the partial pressure of gas x will at some point equal the partial pressure of gas y as gas Y effuses out of the container because at some point the number of particles will be the same