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MCAT chem > equilibrium and thermodynamics > Flashcards

equilibrium and thermodynamics Flashcards

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
what happens to equilbrium if a catalyst is added after the reaction reaches dynamic equilibrium
nothing because catalyst only increases rate of reaction and does not change concentrations of p and r
26
temperature
average kinetic energy
27
kelvin to celcius conversion
K = c +273
28
absolute 0
when temperature is 0K or -273 celcius and has perfect crystal structure/no entropy - all motion stops
29
if two systems are in thermal equilibrium with one another, what kind of heat transfer occurs?
no heat transfer would occur because temperature of each system is the same
30
open system
can exchange heat and matter with sorroundings
31
closed system
energy can be transfered but not matter
32
isolated systems
cant transfer heat or matter with surroundings
33
first law of thermodynamics
applies to closed systems ΔU = Q -ΔW
34
work done by the system
positive
35
work done by the surroundings on the system
negative
36
calorimetry
measure heat exchange
37
caorimetry equation
Q=mcΔT q - heat m - mass c - constant t - temp
38
enthalpy
measurement of heat (J) describes changes to a system gain or loss of thermal energy
39
enthalpy equation
ΔH= ΔU +PΔV u - internal energy
40
internal enthalpy equation
ΔH= ΔU -pΔV
41
q
enthalpy heat gained or lost from the system
42
endothermic
+ΔH requires heat input
43
exothermic
-ΔH releases heat
44
standard enthalpy
1 atm and 25C
45
standard enthalpy of formation
change in enthalpy associated with formation of one mole of compound under standard conditions - always zero for compounds in standard state
46
standard heat of formation
same thing as standard enthalpy of. formation
47
stanard enthalpy of reaction
enthalpy of products - reactants
48
is standard enthalpy a state or path function
state function , does not care about the path, only concerned with the difference in products and reactants
49
bond dissociation energy
enthalpy change associated with breaking bonds ΔHrxn = ΔH (bonds broken)- ΔH (bonds formed)
50
is the formation of bonds exothermic or endothermic
exothermic
51
is bond breakage exothermic or endothermic
endothermic
52
+ΔH
endothermic
53
Hess's law
enthalpy changes in individual steps can be added up to find the total change in enthalpy
54
entropy
the freedom a molecule has to exsist in multiple states - value of disorder
55
what molecules have low entropy
solids
56
what molecules have high entropy
gases
57
second law of thermodynamics
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
what is true of entropy in a completely isolated system
entropy will NEVER decrease, only increase
59
Δs+
positive/ favorable reactions
60
-Δs
decreases in entropy - nonfavorable
61
standard entropy
change in entropy at standard conditions Δsrxn = ΔSp- ΔSr
62
gibbs free energy
maximum amount of work performed by a system - tells spontaneity of rxn - affected by temp, enthalpy, entropy
63
gibbs free energy eqn
ΔG = ΔH- TΔS
64
reaction coordinate diagrams
energy changes associated with a reaction as it is converted from reactants to products
65
transition state
highly unstable, highest energy portion of a reaction aka energy of activation
66
energy of activation
highly unstable and instantaneous barrier to a reaction that must be overcome to complete a reaction
67
ΔG of reaction
energy of products - energy of reactants - determines spontaneity of reaction
68
ΔG+
nonspontaneous reaction endergonic
69
ΔG-
spontaneous reaction exergonic
70
spontaneous
reaction that can proceed without additional force - not affected by enzymes
71
if ΔH is positive and ΔS is negative when is the reactoin spontaneous
never
72
if both ΔH and ΔsS are negative when is ΔG spontaneous
only at low temps
73
if ΔH is - and ΔS is positive when is ΔG spontateous
always
74
gibbs free energy of formation
ΔGp - ΔGr
75
gibbs free energy equillibrium eqn
ΔG = -RTLnKeq
76
thermodynamic product
more stable product ΔG more negative slower and higher energy of activation can be steric hinderance not favored at low temp
77
kinetic product
faster formation with lower activation energy - less stable - low temp
78
which product forms more quickly
kinetic
79
which product forms more slowly
thermodynamic
80
which product is less stable thermodynamically
kinetic
81
which product requires a lower energy of activation
kinetic
82
whihc product is favored at low temperatures
kinetic
83
which product is favored at high temperatures
thermodynamic

MCAT chem (11 decks)

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