Phases and Gases

Question 1

What is stronger, a ion-dipole interaction or a H bond interaction?

Answer 1

ion-dipole interaction is stronger

Question 2

an increase in entropy is a __1__ value, while a decrease in entropy is a __2__ value

Answer 2

1) + 2) -

Question 3

How does an increase in IMF affect density

Answer 3

increase in IMF indicates increased density of a substance

Question 4

Name the process of phase change: 1) solid to liquid 2) liquid to gas 3) gas to solid 4) solid to gas

Answer 4

1) fusion 2) vaporization 3) deposition 4) sublimation

Question 5

When a gas becomes a solid, does KE increase or decrease? How about entropy? Is this an endo or exothermic rxn?

Answer 5

KE decreases entropy decreases exothermic rxn (bcz your forming bonds, which expels energy)

Question 6

What is the triple point and critical point of an phase diagram?

Answer 6

triple point: solid, liquid, and gas of that substance coexist in equillibrium (note this doesn’t necessarily mean in equal amounts) critical point: the point where P & Temp difference between liquid and gas is no longer distinct

Question 7

How does the phase diagram of water differ from the phase diagram of most other substances?

Answer 7

-the slope between solid and liquid is a negative slope, compared to most substances which have a positive slope -this indicates that increased pressure actually promotes the liquid form over the solid form of water (this is because the solid form is less dense than the liquid form). this is the reason why you can glide over ice with ice skates

Question 8

What is calorimetry?

Answer 8

calorimetry measures changes in heat transfer in a chemical rxn

Question 9

Distinguish between a bomb, constant pressure, and low tech calorimeter.

Answer 9

bomb calorimeter: measures energy change at a constant volume (therefore allows for changes in pressure) constant pressure calorimeter maintains constant pressure low tech calorimeter: i.e. coffee cup (which maintains contsant pressure) side note: enthalpy changes are the changes in energy at constant pressures. therefore, you cannot use a bomb calorimeter to measure enthalpy.

Question 10

what is specific heat?

Answer 10

the amount of heat required to raise the temp of 1gram of a substance by 1 degree celsius

Question 11

what is q in q=mc∆T?

Answer 11

q is change in heat, or change in enthalpy (when pressure is held constant)

Question 12

When 2 compounds are reacted together and there is a positive change in temperature (aka temperature increases), does this indicate an exothermic or endothermic rxn

Answer 12

exothermic

Question 13

What are the plateau lines on a heating curve indicate?

Answer 13

the phase changes of that substance. not that these are the areas where heat is added, but the temperature of the substance itself is not increasing. the substance must undergo the phase change before you can further again increase the temperature

Question 14

What is the first plateau and the second plateau of a heating curve indicate

Answer 14

first plateau - heat of fusion second plateau - heat of vaporization

Question 15

Is heat of fusion or heat of vaporization higher in value?

Answer 15

heat of vaporization is always higher in value than heat of fusion for all substances

Question 16

C = mc = heat capacity What is C?

Answer 16

C is usually used and referred to when using a calorimeter

Question 17

The harder it is to raise the temperature of a substance, the ____ (lower or higher) the value of specific heat, c, will be

Answer 17

higher

Question 18

Substance A has a lower specific heat than substance B. Which substance will be easier to raise the temperature of that substance?

Answer 18

Raising the temperature of Substance A will be easier

Question 19

Is the specific heat value for a substance always the same value?

Answer 19

no. the specific heat value will depend on the phase that the substance is in.

Question 20

As a density of a substance increases, the volume of that substance will _____(decrease or increase)

Answer 20

decrease density and volume are inversely related

Question 21

What type of relationship does density have to pressure, temperature, and IMF

Answer 21

Density is directly related to pressure, indirectly related to temperature, and directly related to IMF

Question 22

What is vapor pressure?

Answer 22

the force exerted by the gas particles that vaporize from a solid or liquid sample

Question 23

is vapor pressure affected by external pressure?

Answer 23

no. the vapor pressure is regarding the pressure that the gas of a substance exerts on that substance, which does not include the pressure of the external environment that is exerted on the substance.

Question 24

How is vapor pressure related to temperature and IMF?

Answer 24

vapor pressure is directly related to temperature (as temp increases, vapor pressure increases) vapor pressure is indirectly related to IMF (the more IMF of a substance, aka the more polar the substance is, the less the vapor pressure value will be of that substance)

Question 25

What is the relationship between the vapor pressure of water at sea level compared to the vapor pressure of water on top of Mt Everest

Answer 25

vapor pressure will be the same, as vapor pressure is not affected by external (atmospheric) pressure

Question 26

Boiling Point of a substance occurs when which 2 pressures are equal to each other?

Answer 26

BP occurs when the vapor pressure equals atmospheric pressure

Question 27

How does increased atmospheric pressure affect the BP of that substance?

Answer 27

A higher atmospheric pressure will increase the BP temperature of that substance. i.e. water boils at a higher temperature at sea level than it does on top of Mt Everest

Question 28

Why does it take less energy to boil water at higher altitudes compared to when at sea level?

Answer 28

The vapor pressure of water is constant. The amount of energy required to raise the vapor pressure of water to a lower external pressure is going to require less energy compared to an atmospheric pressure that is higher. Atmospheric pressure is lower at higher altitudes and thus takes less energy to raise the vapor pressure to equal the atmospheric pressure

Question 29

Ethanol has less IMF than water. What does this tell you about the BP of ethanol compared to water?

Answer 29

decrease IMF will decrease the BP. Thus, ethanol will have a lower BP (and lower MP) than water

Question 30

If you increase the pressure of most substances, will this usually increase or decrease the MP/FP?

Answer 30

For most substances, increasing pressure will increase the MP/FP (Note that the most common exception is water)

Question 31

Is pressure directly or inversely related to MP/FP?

Answer 31

For most substances, P is directly r/t MP/FP.

Question 32

The substance with the highest freezing point will have the ____ (lowest/highest) IMF

Answer 32

highest i.e. water has a higher freezing point compared to ethanol. this is because although both are polar molecules, water can create 4 H bonds, while ethanol can only make 3)

Question 33

An ideal gas has ____ IMF

Answer 33

zero meaning that ideal gases do not interact with each other; they do not attract nor repel each other

Question 34

An ideal gas undergoes _____ collisions

Answer 34

elastic (the gas molecules do not lose energy when they collide into the sides of a container; this creates pressure)

Question 35

An ideal gas has an average KE proportional to its ____

Answer 35

temperature

Question 36

Ideality of gases is favored with high temperature and low pressure since interactions of the particles are _____

Answer 36

minimized

Question 37

In addition to noble gases, name 3 other gases that act like ideal gases

Answer 37

N2, H2, O2

Question 38

Avagadros Law: the volume of an ideal gase is proportional to the # particles in the container at a given P and Temp, regardless of the identity of the gas. Therefore, volume of an ideal gas is directly or inversly r/t n (# moles)

Answer 38

directly r/t n

Question 39

1 mole of any ideal gas occupies ____L at STP

Answer 39

22.4 STP = 273K/0celsius and 1 atm

Question 40

Boyles Law

Answer 40

P1xV1 = P2xV2 In other words, P is inversely r/t Volume when at constant temp and #moles (n)

Question 41

Charles Law

Answer 41

V1/T1 = V2/T2 In other words, V and temp are directly related at constant temp and #moles (n)

Question 42

What is the ideal gas law?

Answer 42

PV = nRT

Question 43

1 atm = ____ kPa = ____ torr = ____ mm Hg

Answer 43

101kPa 760 torr 760 mm Hg

Question 44

1L = 1000mL = ____cm^3 = ____m^3

Answer 44

1000 cm^3 0.001 m^3

Question 45

What is the volume of 0.25mol He @ 25 degrees Celsius & 725 torr?

Answer 45

instead of converting torr to atm and using PV = nRT equation, it is good enough in this instance to estimate STP values: 0 degrees celsius and 760 torr. At STP, 1 mol gas = 22.4L. Therefore, 0.25mol @ STP = 22.4 x 1/4 = 5.5L Real value = 6.2

Question 46

How do real gases compare to ideal gases in relation to IMF and collisions?

Answer 46

real gases are influenced by IMF and their frequency of collisions are NOT elastic, thus their collisions with the side of the container decrease pressure. the pressure of an ideal gas is greater than the pressure of a real gas

Question 47

How does the volume of an ideal gas compare to the volume of a real gas

Answer 47

V ideal > V real This is because real gases have a physical size and take up space in the container; therefore free space in the container is smaller

Question 48

In the real gas law, what do a and b stand for

Answer 48

a = attraction force of molecules to each other (increased IMF increases a) b = “bigness” of the gas molecules

Question 49

Of F2 and Cl2, which one will be more likely to act like an ideal gas?

Answer 49

F2 because it is smaller in size

Question 50

How is Partial pressure, P_a, of a gas calculated?

Answer 50

P_a = X_a x P_total

X_a = mole fraction of substance = # moles of a molecule / total # of moles in substance

If calculating P_a at STP, then P_a = X_a because P_total = P_atm = 1 atm

Question 51

Do heavier or lighter gas particles move more quickly?

Answer 51

Lighter gas molecules move more quickly than heavier gas molecules