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MCAT Chemistry by me > Phases > Flashcards

Phases Flashcards

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1
Q

what is the standard temperature and pressure

A

1 atm and 273 K

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2
Q

what is the mean free path

A

a free path traveled by a molecule before a collision

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3
Q

how the polarity differences between molecules affect gas and liquid

what does polarity difference mean for homogeneity for liquids and gases

A

the polarity difference doesn’t matter much in gases because the molecules are so far apart that there is negligible attractive or repelling forces. On the other hand, polarity difference matters a lot for liquids b/c the molecules are relatively closer

the polarity difference makes a difference in whether or not a substance is homogeneous. because polarity difference doesn’t matter much for gases, a gas mixture is homogeneous and miscible with other types of gases

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4
Q

Is gas miscible with other gases? how do different gases separate?

A

gases separate based on densities

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5
Q

what does kinetic molecular theory predict about ideal gases

A

no attractive force

no molecular volume

elastic collisions

the average kinetic energy is directly proportional to the temperature

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6
Q

in a simple mercury barometer, how do you measure the pressure?

A

P = density * g * h

the density of mercury is given
the height above the bath indicates the atmospheric pressure

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7
Q

how are pressure and temperature related to kinetic energy of the gas?

A

pressure is the kinetic energy per volume of gas

temperature is the average kinetic energy per mole of molecules

so the pressure and temperature are directly related

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8
Q

how is the volume of gas related to the temperature of gas

A

directly related

increase in temperature causes increase in the volume of gas

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9
Q

what does insulation mean

what does a completely insulated setting mean? what does an open environment mean?

A

heat is not exchanged between the system and surrounding.

in a completely insulated setting, only work is transferred

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10
Q

at STP, how much volume does one mole of gas occupy?

A

one mole of gas occupies 22.4 L of volume

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11
Q

how do you calculate the partial pressure equilibrium constant?

A

Kp = (Pressure of product^ mole of that product)/ (pressure reactant ^ mole of that reactant)

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12
Q

how is the partial pressure equilibrium related to the concentration equilibrium constant of the same reaction?

A

directly related but the partial pressure equilibrium constant is times temperature *R to the power of change in moles of products and reactants

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13
Q

how do real gases deviate from ideal gases

A

real gases occupy volume and exert attractive forces on one another

therefore, the volume is bigger and pressure is less

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14
Q

in what pressure and temperature is the gas likely to act like a real gas?

A

low temperature and high pressure when the molecules are close together

low temperature brings the molecules close together; thus, makes the molecules exert attractive forces

high pressure also brings the molecules closer together, causing the volume of the molecules non-negligible compared to the volume of the container

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15
Q

what is the PV/RT = n, for a gas at ideal condition?

A

1

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16
Q

what does it mean when PV/RT = n > 1 or PV/RT = n

A

positive deviation implies that the pressure is high, meaning that the high pressure causes the volume of molecules to be significant –> deviation due to volume

negative deviation implies that the deviation is due to increase in temperature. increase in temperature makes the gas molecules to exert attractive forces –> deviation due to attractive intermolecular forces

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17
Q

what is heat capacity qualitatively and quantitatively?

A

the added energy required to increase the temperature of the given substance by one kelvin

how much resistance a substance has to absorbed heat. depends on the degrees of freedom: how much stretching of intermolecular bonds, rotating, vibrating, and etc a substance can do to absorb energy without increasing its temperature

C = q/ change in temperature = J/K

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18
Q

how much is one 1 in joules?

A

4.2 joules. about 4 joules.

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19
Q

how is the heat of water related to heat of the reactants in a calorimeter?

A

q water = -q reactants

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20
Q

coffee cup calorimeter condition: what are the pressure and insulation conditions?

A

constant pressure of the atm so H can be substitute for q

insulated to prevent heat exchange with the surrounding so the change in temperature of water directly related to change in energy

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21
Q

what does a bomb calorimeter measure?

what are the conditions of bomb calorimeter like?

A

rigid and thermally insulated

it measures change in internal energy

change in internal energy = heat when no work is done

volume does not change so no work

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22
Q

what kind of property is heat capacity?

A

extrinsic, depends on the amount

heat capacity can increase if you have a lot more mass

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23
Q

how is change in enthalpy related to q = mc*change in temperature?

A

change in enthalpy is negative of q = mc*change in temperature

heat transferred into the calorimeter (positive) is equal to the heat released by the reaction (negative)

24
Q

what’s wrong in thinking that melting and boiling points are actual “points”?

A

melting and boiling points are on a continuum that changes depending on the pressure. So the melting and boiling points are rather curves than points

25
Q

in a T = q/mc graph of phase change, what is the slope

what does it mean when the slope is zero?

A

slope is 1/mc

when the slope is zero, that means the substance is undergoing change a change. this may mean a heat of vaporization, fusion, sublimation. - phase change - in solid/liquid or liquid/gas phase with increase in heat/q

26
Q

in a phase diagram, P vs. T, what does the line indicate?

A

the line between the states indicate that the states are in equilibrium with one another

27
Q

what is a triple point in a phase diagram, P vs T?

A

that means all the states, solid, liquid, and gas are in equilibrium

28
Q

critical temperature

A

temperature above which a substance cannot be liquefied regardless of the pressure

29
Q

critical pressure

A

pressure required to produce the liquid phase when the substance is at the critical temperature

30
Q

critical point

A

critical pressure and critical temperature together

31
Q

supercritical fluid

A

fluid beyond the critical point having characteristics of both liquid and gas

32
Q

in a phase diagram, what does the slope between states indicate?

A

P/T = nR/V

moles*R per volume - the slope indirectly indicates density

the negative slope indicates that the solid is less dense than water

33
Q

what is the heat capacity when there is a change in phase?

A

infinite

heat is added but temperature change remains zero. no change in temperature

34
Q

melting and boiling point assumes what is constant

A

pressure is constant so heat of enthalpy is equal to heat

35
Q

does each phase of a substance has its own specific heat capacity? what does this mean in terms of the q=mcT graph?

A

Yes. this means each phase has a unique “c”, heat capacity in the graph q=mcT, when you graph T vs. q

36
Q

why does gas have much lower specific heats than solid or liquid?

A

because the intermolecular bonds are pretty much non-existant in gases so the energy can be put into increasing their kinetic energy, not breaking up the INTM bonds like for solids and liquids

37
Q

sublimation vs deposition

A

sublimation: solid to gas
deposition: gas to solid

38
Q

what is a phase diagram

A

shows the pressure and temperature at which different phases exist for a particular substance

39
Q

in a phase diagram, what pressure and temperature does a solid, liquid, and gas generally at?

A

mainly temperature that dictates the phase

solid - very low temperature and high pressure - when molecules are close together

liquid - average P and T, but definitely must be above a particular pressure to be a liquid

gas - at very low pressure and very high temperature, definitely exists as a gas

40
Q

Examples of colligative properties

A

Freezing and boiling points

Vapor pressure

Osmotic pressure

41
Q

why is heat capacity at constant pressure higher than the heat capacity at constant volume?

A

because in constant volume, the substance cannot expel the energy as work

42
Q

why does increase in temperature decrease the solubility of gas?

A

because increase in temperature causes the gas molecules to break from their intermolecular bonds and escape the liquid

43
Q

Henry’s law states that solubility of gas is related to what?

A

increase in pressure. c, solubility of gas, is equal to partial pressure of gas and k constant that is intrinsic to the substance

44
Q

what is a van’t hoff factor

A

effect on solutes for colligative properties like vapor pressure, boiling point elevation, and freezing point depression, and osmotic pressure

45
Q

in a heating curve graph of T vs. q, where can you find the boiling point and melting point of a liquid?

A

in the beginning of liquid line - melting point

end of the liquid line - boiling point

46
Q

what enthalpy is bigger, heat of vaporization or heat of fusion?

A

heat of vaporization because the intermolecular bonds must be completely broken

47
Q

in the phase diagram for water, is 1 atm below or above the triple point?

A

1 atm is at least equal or above the triple point because at 1 atm water can be solid, liquid, or gas depending on the temperature

triple point is the point where the substance can be solid, liquid, or gas in equilibrium at a specific pressure and temperature. So it has to be below 1 atm

48
Q

pressure and temperature of solid, liquid, and gas

knowing where the solid, liquid, and gas are in the phase diagram

A

solid can be at any pressure but at lower temperature

liquid must be above a certain pressure in between, but higher temperature than solid and lower temperature than gas

gas is generally at high temperature and low pressure, conditions of an ideal gas

49
Q

what does the negative slope between solid and liquid in the phase diagram of water indicate?

A

density of liquid is greater than the density of solid - why ice floats on water

density increases with increase in pressure - mass stays the same but the molecules are pushed together so the volume decreases.

50
Q

what is a critical point in the phase diagram

A

point from on when the gas and liquid cannot be distinguished from one another

have the same density

coexist as gas and liquid at equilibrium and is called a supercritical fluid

51
Q

what is a colligative property

A

property that depends on the amount, how many molecules you have, not the kind of molecules

52
Q

what is osmotic pressure?

what is it referred to in terms of energy? what is this energy for pure water vs. salt water?

under constant pressure and temperature, how do things from according to osmotic pressure?

A

iMRT

inward pulling force by the solutes in the solution

difference in pressure created by the solvent migration in a semi-permeable membrane

system’s free energy, pure water has an osmotic potential of zero while salt water has a negative osmotic potential

under constant pressure and temperature, things flow from high osmotic potential to low osmotic pressure

53
Q

why do solids and liquids have greater heat capacity than gas?

A

because less energy goes into increasing the KEavg (Temperature)

when attracted molecules become farther apart, the potential energy increases. expansion of solid or liquid implies that the potential energy is increasing

54
Q

at what pressure and temperature are the molecules pushed closer together?

A

high pressure and low temperature

55
Q

bomb calorimeter

what is it?
does the volume change?
what does it measure?

A

combustion reaction in a rigid container with water surrounding it.

the volume is constant so no work is done

figure out internal energy of a reaction

measures the heat of the reaction which is heat capacity * change in temperature

56
Q

coffee cup calorimeter

what does it measure?
does the volume change?

A

measures the heat flow at constant pressure through the temperature difference in water

volume is constant so no work is done

heat of flow can be found by masscTchange

MCAT Chemistry by me (8 decks)

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