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MCAT chem > equilibrium and thermodynamics > Flashcards

equilibrium and thermodynamics Flashcards

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1
Q

reaction reversibility

A

products are converted to reactants at the same time reactants are converted to products

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2
Q

rate of chemical reaction depends on what

A

amount of reactant present

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3
Q

dynamic equilibrium

A

where the forward reaction occurs at the same rate as the reverse reaction and there is no change in reactant/product concentration

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4
Q

equilibrium constant K eq

A

[p]/[r]

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5
Q

what does a keq> 1 mean

A

products> reactants so the product is favored
- will go in forward direction

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6
Q

what does a keq<1 mean

A

reactants are favored and reaction will go in the reverse reaction

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7
Q

when calculating keq, what is ommited?

A

pure liquids (h2O) and pure solids

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8
Q

keq of forward related to reverse

A

inverse –> 1/Keq

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9
Q

can keq be negative

A

no, concentrations of p and r are not negative

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10
Q

what is equillibrium constant dependent on

A

concentrations of product/reactant and temperature

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11
Q

rection quotient

A

same as the equation for equilibrium constant but the concentrations can be used from any time, not just at equilibrium
- still should not include pure liquids and solids

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12
Q

purpose of reaction quotient

A

predicts which direction an equation will move in order to establish equillibrium

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13
Q

when Q < Keq

A

the ratio of products to reactants is lower than at equillibrium so the equation is pushed in the forward direction

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14
Q

when Q > Keq

A

the ratio of products to reactants is higher than it would be at equilibrium so it is pushed in the reverse reaction

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15
Q

when Q = Keq

A

reaction has reached dynamic equilibrium

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16
Q

le chatlier’s principle

A

when equilibrium is disrputed, the reaction will move in the direction that favors the restoration of equ.

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17
Q

if excess reactant is added how does the system correct equillibrium?

A

form more product
- reaction shifts forward

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18
Q

if reactant is removed how does the system correct equillibruim

A

favors the reverse reaction to make more reactant

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19
Q

if product is added how does the system correct equilibrium

A

favors reverse reaction

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20
Q

if product is removed how does the system correct equilibrium

A

favors forward reaction

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21
Q

what happens to a system if the volume is increased

A

pressure is decreased
- shifts toward the side with more moles of gas

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22
Q

what happens to a system if the pressure is increased

A

volume decrease
- shift toward side with less moles of gas

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23
Q

what happens to reestablish equilibrium when temperature is added

A

if ΔH> 0 shift toward products if ΔH< 0 shift toward reactants

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24
Q

what happens to reestablish equilibrium if temperature is reduced

A

if ΔH> 0 shift toward reactants if ΔH< 0 shift toward products

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25
Q

what happens to equilbrium if a catalyst is added after the reaction reaches dynamic equilibrium

A

nothing because catalyst only increases rate of reaction and does not change concentrations of p and r

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26
Q

temperature

A

average kinetic energy

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27
Q

kelvin to celcius conversion

A

K = c +273

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28
Q

absolute 0

A

when temperature is 0K or -273 celcius and has perfect crystal structure/no entropy
- all motion stops

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29
Q

if two systems are in thermal equilibrium with one another, what kind of heat transfer occurs?

A

no heat transfer would occur because temperature of each system is the same

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30
Q

open system

A

can exchange heat and matter with sorroundings

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31
Q

closed system

A

energy can be transfered but not matter

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32
Q

isolated systems

A

cant transfer heat or matter with surroundings

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33
Q

first law of thermodynamics

A

applies to closed systems
ΔU = Q -ΔW

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34
Q

work done by the system

A

positive

35
Q

work done by the surroundings on the system

A

negative

36
Q

calorimetry

A

measure heat exchange

37
Q

caorimetry equation

A

Q=mcΔT
q - heat
m - mass
c - constant
t - temp

38
Q

enthalpy

A

measurement of heat (J)
describes changes to a system
gain or loss of thermal energy

39
Q

enthalpy equation

A

ΔH= ΔU +PΔV
u - internal energy

40
Q

internal enthalpy equation

A

ΔH= ΔU -pΔV

41
Q

q

A

enthalpy
heat gained or lost from the system

42
Q

endothermic

A

+ΔH
requires heat input

43
Q

exothermic

A

-ΔH
releases heat

44
Q

standard enthalpy

A

1 atm and 25C

45
Q

standard enthalpy of formation

A

change in enthalpy associated with formation of one mole of compound under standard conditions
- always zero for compounds in standard state

46
Q

standard heat of formation

A

same thing as standard enthalpy of. formation

47
Q

stanard enthalpy of reaction

A

enthalpy of products - reactants

48
Q

is standard enthalpy a state or path function

A

state function , does not care about the path, only concerned with the difference in products and reactants

49
Q

bond dissociation energy

A

enthalpy change associated with breaking bonds
ΔHrxn = ΔH (bonds broken)- ΔH (bonds formed)

50
Q

is the formation of bonds exothermic or endothermic

A

exothermic

51
Q

is bond breakage exothermic or endothermic

A

endothermic

52
Q

+ΔH

A

endothermic

53
Q

Hess’s law

A

enthalpy changes in individual steps can be added up to find the total change in enthalpy

54
Q

entropy

A

the freedom a molecule has to exsist in multiple states
- value of disorder

55
Q

what molecules have low entropy

A

solids

56
Q

what molecules have high entropy

A

gases

57
Q

second law of thermodynamics

A

in an isolated system, entropy inevitably increases
- in a heat transfer the molecules will move randomly and favorably from high temp to low temp

58
Q

what is true of entropy in a completely isolated system

A

entropy will NEVER decrease, only increase

59
Q

Δs+

A

positive/ favorable reactions

60
Q

-Δs

A

decreases in entropy
- nonfavorable

61
Q

standard entropy

A

change in entropy at standard conditions
Δsrxn = ΔSp- ΔSr

62
Q

gibbs free energy

A

maximum amount of work performed by a system
- tells spontaneity of rxn
- affected by temp, enthalpy, entropy

63
Q

gibbs free energy eqn

A

ΔG = ΔH- TΔS

64
Q

reaction coordinate diagrams

A

energy changes associated with a reaction as it is converted from reactants to products

65
Q

transition state

A

highly unstable, highest energy portion of a reaction
aka energy of activation

66
Q

energy of activation

A

highly unstable and instantaneous barrier to a reaction that must be overcome to complete a reaction

67
Q

ΔG of reaction

A

energy of products - energy of reactants
- determines spontaneity of reaction

68
Q

ΔG+

A

nonspontaneous reaction
endergonic

69
Q

ΔG-

A

spontaneous reaction
exergonic

70
Q

spontaneous

A

reaction that can proceed without additional force
- not affected by enzymes

71
Q

if ΔH is positive and ΔS is negative when is the reactoin spontaneous

A

never

72
Q

if both ΔH and ΔsS are negative when is ΔG spontaneous

A

only at low temps

73
Q

if ΔH is - and ΔS is positive when is ΔG spontateous

A

always

74
Q

gibbs free energy of formation

A

ΔGp - ΔGr

75
Q

gibbs free energy equillibrium eqn

A

ΔG = -RTLnKeq

76
Q

thermodynamic product

A

more stable product
ΔG more negative
slower and higher energy of activation
can be steric hinderance
not favored at low temp

77
Q

kinetic product

A

faster formation with lower activation energy
- less stable
- low temp

78
Q

which product forms more quickly

A

kinetic

79
Q

which product forms more slowly

A

thermodynamic

80
Q

which product is less stable thermodynamically

A

kinetic

81
Q

which product requires a lower energy of activation

A

kinetic

82
Q

whihc product is favored at low temperatures

A

kinetic

83
Q

which product is favored at high temperatures

A

thermodynamic

MCAT chem (11 decks)

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