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MCAT > GChem: Phases and Gases > Flashcards

GChem: Phases and Gases Flashcards

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MCAT flashcards
1
Q

Vaporization, fusion, deposition, sublimation, condensation, crystallization

A

Vaporization (liquid to gas), fusion (solid to liquid), deposition (gas to solid), sublimation (solid to gas), condensation (gas to liquid), crystallization (liquid to solid)

The heat of vaporization is same mag but opp side of heat of condensation, etc (either heat released or absorbed)

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2
Q

What is variable for heat capacity? What equation is it in?
Specific heat? units?
Molecules with _______ tend to have high specific heats

A

heat capacity = C
q = CΔT
q = mcΔT
little c = specific heat -> resistance to change in temp
units -> J/gºC or J/gK (or cal/gºC if other units match)
Molecules with strong intermolecular forces tend to have high specific heats

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3
Q

1 cal = ____J

A

1 cal = 4.2J

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4
Q

*Non flat slope of heating curve represents______(what variable/expression?)
water melts at ___and boils at ____

A

Slopes represent 1/C, the reciprocal of the substance’s heat capacity in that phase
water melts at 0ºand boils at 100º

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5
Q

How much heat (in calories) is necessary to raise the temp of 2g of solid H2O from 0ºC to 85º? Heat of fusion of water = 80cal/g and the specific heat of water is 1cal/gºC

A

330cal pg. 150 GChem, need to take into account temp increase and phase change equations

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6
Q

Given that each of the following solutions is at equilibrium with its environment, which solution should have the lowest temperature?

a) solution 1% ice and 99% water
b) solution 99% ice and 1% water
c) all these solutions will have the same temp

A

answer c bc remember graph where during phase change temperature does not change

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7
Q

Phase diagram: what is the triple point, critical point?
Draw one out with sections for liquid, solid, gas
What does the boundary line b/w phases represent?
What do the intersections represent when we draw a horizontal line across graph where 1 atm is?
Super critical fluid? What is special about it?

A

Triple point -> temp and pressure which all three phases exist at same time at equilibrium and therefore all phase changes happen simultaneously
Critical point -> marks end of the liquid-gas boundary, beyond this point, the substance displays properties of both a liquid (such as high density) and a gas (low viscosity), liquid and gas phases are no longer distinct = supercritical fluid, no amount of pressure can force it into its liquid phase
Boundary lines rep points at which the two phases are at equilibrium
ex. solid/liquid boundary represents trend in fp/mp and liquid gas boundary rep trend in bp
Horizontal line at 1 atm crosses temp of melting and boiling point

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8
Q

How is the water phase diagram different than everyone else?

A

There is a slight neg slope for the solid liquid boundary line so for H2O, an increase in pressure at constant temp can favor the liquid phase, not the solid phase
Think about ice skater, as blade of ice skater contacts the ice, the pressure increases, melting the ice under the blade and allowing the skate to glide over the liquid water

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9
Q

For H2O:

Density of _____ is less than density of ______

A

Weird bc density of ice is less than density of water

ice floats in glass of water

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10
Q

For conversions:

1 mol gas = _____ L

A

22.4 L

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11
Q

Page 155 GChem Q6

A

Use logic

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12
Q

Characteristics of ideal gas

KE of particles is proportional to:______

A

Two main characteristics: weakest IMFs, smallest volume (so takes up less free space)
Takes up no volume
Particles move at constant speeds, random directions
When collide with wall this represents the pressure of the gas (pressure is ONLY due to collisions with wall), collisions with wall and each other are elastic so KE is conserved
Molecules experience no IMFs
KE of particles is proportional to temperature

V -> free space, not volume of container

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13
Q

1L = ____mL = ____ cm^3 = ____ m^3

OR

1cm^3 = \_\_\_cc = \_\_\_mL = \_\_\_g
1m^3 = \_\_\_\_L
A

1L = 1000 mL = 1000 cm^3 = 0.001 m^3

1cm^3 = 1cc = 1mL = 1g
1m^3 = 1000L
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14
Q

Equation to convert ºC to K

USE K WITH GASES!

A

T (in K) = T (in ºC) + 273.15

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15
Q

Different values for pressure (4)

A

1 atm = 760 torr = 760 mm Hg = 101 kPa

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16
Q

What would be the reading of a barometer (measures pressure) filled with a liquid of lower density than Hg if at that moment another nearby Hg barometer reads 752 mm Hg?
Less than 752 mm, 752 mm, greater than 752 mm, it depends on the compressibility of the liquid

A

Pg 162 GChem - Greater than 752 mm

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17
Q

Ideal gas law equation, the iconic one and units for each

what is the volume for that constant?

A 
Pv=nRT
P -> pressure (atm) 
V -> volume of container (L)
n -> moles of gas
R -> universal gas constant 0.0821 L-atm/K-mol (or 8.3 J⋅K−1⋅mol−1 but pretty sure first one's used more) 
T -> temp of gas (K)
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18
Q

Argon, at a pressure of 2 atm, fills a 100mL vial at a temp 0ºC. What would the pressure of the argon be if we increase the volume to 500mL, and the temp is 100ºC?

A 
Pg 163 GChem 
P2 = 0.55 atm 
make equation:
PV/T = PV/T
bc their nR should we equivalent 
MAKE SURE TO CONVERT TO LITERS AND KELVIN
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19
Q

Charles’s Law (about gases)

A

P inversely proportional to V
P ∝ 1/V if temperature is constant
Makes sense with PV=nRT

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20
Q

Boyle’s law

A

P ∝ T if volume constant

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21
Q

If only n is constant we get the combined gas law:
Also rule for what ever is held constant, you need to isolate that with nR on one side of the equations and equate whats left over between the two senarios

A

PV/T = PV/T

For rule can see pg 164 GChem for example

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22
Q 
Equations relating to PV=nRT 
at:
Constant P: 
Constant T: 
Constant V:
A

ANY OF THESE OR FLIP WHOLE FRACTION
Constant P: V/T = V/T
Constant T: PV=PV
Constant V: P/T = P/T

23
Q

*What is the volume of one mole of any ideal gas at 0ºC and 1 atm = ______

A

22.4 L

24
Q

How to find limiting reagent?

A

divide moles by coefficient

25
Q

If have equation with only gases, then can treat coefficients like____

A

moles

26
Q

STP?

A

1 atm, 273K or 0ºC, 22.4L (for gases)

27
Q

*Ideal gases favor _____ pressure and ______ temperatures

A

low pressures and high temperatures

28
Q

*Ideal gases favor _____ pressure and ______ temperatures so under the opposite conditions,

A

low pressures and high temperatures

29
Q

Fill in ideal gas or real gas
P____< P_____
V____< V_____

A

P real < P ideal (real gases have more IMFs so collide less with walls)
V real < V ideal (real gas particles do have volume so the free space in the container is smaller)
Remember: IDEAL WORLD IS BETTER THAN THE REAL WORLD

30
Q

In the van der waals equation, one can account for real gas behavior
(P + (an^2/V^2))(V - nb) = RT
The (P + (an^2/V^2)) term takes into account…
The (V - nb) term…

A

The (P + (an^2/V^2)) term takes into account attraction b/w real gas particles
- a increases as the IMFs of a gas get stronger

The volume term (V-nb) accounts for the volume occupied by the real gas particles
- b increases as the size of the gas particles increase

31
Q

Which of the following gas would behave most like an ideal gas if all were at the same temperature and pressure?
H20, CH4, HF, NH3

A

CH4 bc weakest IMF, dispersion forces

32
Q

Dalton’s Law of partial pressures:

How to find the partial pressure of a gas:

A

P total = Pa + Pb + Pc
P partial = X (P total)
X -> mole fraction = moles or particles of gas/ total moles or particles of gas

33
Q

A vessel contains a mixture of three gases: A, B, C. There is twice as much A as B and half as much C as A. If the total pressure is 300 torr, what is the partial pressure of Gas C?

a) 60 torr
b) 75 torr
c) 100 torr
d) 120 torr

A

pg 171
75
can draw out and see that B=C and then use answer choices to plug in values to equal P total

34
Q

Whenever see gas leaving something ;)

Graham’s Law of Effusion:

A

rate of effusion of Gas A/ rate of effusion of Gas B = square root of (molar mass of Gas B/ molar mass of Gas A)

rate of effusion can also be called root mean square (rms) which is the square root of the mean of the square of speed so it basically represents average speed of molecules

35
Q

At same temperature, do lighter or heavier molecules travel faster? How do their KE compare?

As temperature increases, average speed_____
At the same temperature, they have the same____

KE is directly proportional to temperature IN KELVINS!!

A

Lighter molecules travel faster bc KE depends on both mass and speed
At same temperature they have the same KE
As temperature increases, average speed increases, but not all molecules of that same gas move at the exact same speed

36
Q

For water, as increase pressure, what happens to mp/fp?

A

Remember the graph with different phases As increase pressure (y-axis) the mp/fp decreases (bc slope neg for water which is unusual)

37
Q

Density is a measure of how condensed a substance is: D = m/v
Below will either be directly or inversely
External P is _____ proportional
External T is ______ proportional
IMF is _______proportional

A

common sense
External P is directly proportional to density
External T is inversely proportional
IMF is directly proportional

38
Q

What is vapor pressure?
Indicated proportionality or no effect of the following:
External P on vapor pressure, External T, IMF

A

Vapor pressure is force exerted by the gas particles that vaporize from a solid or liquid sample
Vapor pressure is property of the liquid so external pressure has no effect on vapor pressure,
External T is directly proportional to vapor pressure, and IMF is inversely proportional to vapor pressure

39
Q

What is vapor pressure?
Indicate the proportionality or no effect of the following:
External P on vapor pressure, External T, IMF

A

Vapor pressure is force exerted by the gas particles that vaporize from a solid or liquid sample
Vapor pressure is property of the liquid so external pressure has no effect on vapor pressure,
External T is directly proportional to vapor pressure, and IMF is inversely proportional to vapor pressure
Vp is like volatility

40
Q

Boiling point is (direct definition and simple equation)
Indicate the proportionality or no effect of the following:
External P on bp, and IMF

The less the difference between ___ and ____, the easier it is to boil

A

Bp is the temp at which the condensation/vaporization phase transitions occur and specifically when vapor pressure = atmospheric pressure so the smaller the different b/w bp and atm p, the easier it is to boil
External P is directly proportional to bp (remember phase diagram pos slope)
IMF is directly proportional

41
Q

*Melting/freezing point (mp/fp) is:
Indicate the proportionality or no effect of the following:
External P and IMF on mp/fp

A

Melting/freezing point (mp/fp) is the temperature at which the fusion/crystalization phase transitions occur
External P -> directly proportional to mp/fp (except for water)
IMF is directly proportional to mp/fp

42
Q

For what type of molecules can dispersion forces be particularly strong?
Tip: if asked for highest freezing point, highest vp, etc then look at IMF strength and cross out two middle strength ones bc it will always be an extreme

A

Halogens
ex. Like F2, Cl2, etc they can have dispersion forces to other molecules -> F2 can have dispersion forces with another F2

43
Q

Difference b/w non-electrolyte, weak electrolyte, strong electrolyte

A

Strong electrolyte -> complete dissociation
like strong acid, strong base
Weak electrolyte -> partial dissociation in water
Non-electrolyte -> no dissociation in water

44
Q

What is van’t Hoff factor?

A

van’t Hoff factor (i) is the number of particles produced in solution per mole of substance
It helps us understand electrolyte
C6H12O6 i = 1 non electrolyte, 1 bc stays together/ does not dissociate
HF 1<i></i>

45
Q

What happens to electrolytes in water, polar non-electrolytes in water, nonpolar non-electrolytes in water

A

Electrolytes dissolve in water: 1) agitation (stirring which is endothermic)2) Dissociation (endothermic) 3) solvation (exothermic)
Polar non-electrolytes: dissolve - think sugar in water when you have to stir A LOT to get it to dissolve 1) agitation (endothermic) 2) solvation (exothermic)
Nonpolar non-electrolyte do not dissolve in water: 1) agitation (endothermic) and that’s it

Have solvation when can form strong IMFs with water - LIKE DISSOLVES LIKE

46
Q

What happens when add solvent to saturated solution and super saturated solution?

A

In saturated solution, no additional solute will dissolve

With super saturated solution additional solute causes excess to precipitate

47
Q

Solid and liquid solutes in water

Relationship (direct or inverse) to temperature and pressure

A

Solid and liquid solubility is directly proportional to temperature
Solubility is not affected by pressure

Throwing sugar into iced tea vs hot tea (dissolves quicker)

48
Q

Gaseous solutes in water

Relationship (direct or inverse) to temperature and pressure

A

Gaseous solubility is indirectly proportional to temperature
Gaseous solubility is directly proportional to pressure

For gas in water ex. Soda
Warm soda goes flat faster bc CO2 comes out of solution
For gas and pressure imagine what happens when open can (when lower pressure and open, a bunch of gas comes out of solution)

49
Q

ALWAYS soluble:

Usually insoluble:

A

ALWAYS soluble is group I ions, NH4+, NO3-, CH3COO-, ClO4-

Usually insoluble unless attached to something above: Ag+, Pb2+, Pb4+, Hg22+, Hg2+, CO32-, PO43-, S2-

50
Q

A 2 mol sample of He initially at 1 atm and 27ºC has its temp doubled and its volume halved. What is the final pressure of the gas?

A

Isolate pressure on one side and see that when all the changes are taken into account the right side of the equation is basically multiplied by 4 and 4 time 1 = 4

51
Q

What is the partial pressure of He in a mixture comprised of 2 g He, 32 g O2 and 44 g CO2at STP?

A

Convert each to moles to get mole ratio

then use 1 atm for total pressure bc at STP

52
Q

**If something is volatile it has high ______

Salts are stable at high/low temperatures

A

vapor pressure!

Salts are stable at high temperatures

53
Q

*Avogadro’s number concept?

A

If two equal-volume containers hold gas at the same temperature and pressure, then they contain the same number of particles (regardless of identity of the gas).

54
Q

_________ atoms and molecules exhibit stronger dispersion forces.

What kinds of E do real and ideal gases have?

A

Larger and heavier atoms and molecules exhibit stronger dispersion forces than smaller and lighter ones.
This is because easier to have temporary dipole

Real gases have potential (bc of IMFs) and kinetic E, while ideal gases have kinetic E

MCAT (36 decks)

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