Ch 2 exam Flashcards

1
Q

the half life of a ____ order reaction is constant.

A

first

t1/2 = ln 2/k

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2
Q

the half life of a reaction depends on the ____

A

order of the reaction

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3
Q

rate of a first order reaction

A

rate = k [A]

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4
Q

rate of a zero order reaction

A

rate = k

i.e. rate = k[A]^0 = k

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5
Q

the half life of a zero order reaction DOES DEPEND on ____

A

the initial concentration of the reactant

t1/2= [A]0/2k

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6
Q

the half life of a second order reaction DOES DEPEND on ____

A

the initial concentration of the reactant

t1/2 = 1/k*[A]0

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7
Q

collision theory

A

reactants must collide in order to react with each other

1) rate of reaction is proportional to the rate of reactant collisions
2) molecules must be oriented properly when they collide
3) molecules must have adequate kinetic energy to react (activation energy)

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8
Q

Ea

A

activation energy

minimum energy necessary to form a product during a collision between reactants

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9
Q

catalyst

A

a substance that increases the rate of a chemical reaction by lowering the activation energy without itself being consumed

catalyst is regenerated in the process

provide an alternate reaction pathway with a lower activation energy

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10
Q

homogeneous catalyst

A

in the SAME PHASE as the reactants. it speeds up the reaction by forming a reactive intermediate.

the reactive intermediate reacts further to form a product and regenerate the catalyst. the reactive intermediate is formed but immediately consumed.

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11
Q

heterogeneous catalyst

A

in a different phase from that of the reactants.

usually the catalyst is a solid and the reactants are gas or liquid

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12
Q

enzyme

A

biological HETEROGENEOUS catalyst

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13
Q

reaction mechanism

A

the series of reactions that occurs to produce the overall observed reaction

most reactions occur in a series of small reactions involving one, two, or (at most) three molecules.

knowing the rate law of the reaction helps us determine the sequence of reactions in the mechanism

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14
Q

intermediates

A

materials that are products in an early mechanism step, but then reactants in a later step

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15
Q

molecularity

A

the number of reactant particles in an elementary step

unimolecular = one particle
bimolecular = two particles (can be the same type of particle)
termolecular = three particles

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16
Q

rate law for an overall reaction must be determined ____

A

experimentally

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17
Q

rate determining step

A

slowest step

the rate law of the rate determining step determines the rate law of the overall reaction

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18
Q

chemical equilibrium

A

rates of both reaction and reverse reaction are equal

no further changes in concentration of either gas occurs unless the temperature or the volume of the container is changed

does NOT mean the amount of reactants and products are equal (just rates)

this is DYNAMIC equilibriumr

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19
Q

reaction quotient, Q

A

mathematically expression of the the amounts of reactants and products present at any given point in a reversible reaction

can vary prior to equilibrium

can be calculated at any point in the reaction

often calculated at the start of the reaction using initial concentrations

20
Q

Qc vs Qp

A

Qc = amounts expressed in concentration; Molarity

Qc = [C]^c[D]^d / [A]^a[B]^b

Qp = partial pressures

Qp = P(C)^cP(D)^d / P(A)^aP(B)^b

21
Q

equilibrium constant, K

A

the value of Q when the reaction is at equilibrium

Kc = Qc at equilibrium

K is unitless

22
Q

law of mass action

A

states that the values of the equilibrium constant expressions are a constant for a particular reaction, at a given temperature

the relationship between the chemical equation and concentrations of reactants and products

23
Q

The value of the equilibrium constant K is independent of:

A

the starting amounts of reactants and products

24
Q

The value of the equilibrium constant K is dependent on:

A

the temperature of the system

25
the magnitude of an equilibrium constant indicates:
the extent of a reaction
26
K and Q are
unitless
27
If K is very small:
the mixture contains mostly reactants at equilibrium
28
If K is very large:
the mixture contains mostly products at equilibrium
29
The value of K gives no indication as to:
whether the reaction is fast or slow
30
K (backward) =
1/K (forward)
31
Q
reaction forms products; shift R
32
Q>K
reaction forms reactants; shift L
33
Q=K
equilibrium
34
homogenous equilibrium
all the reactants and products are present in the same phase
35
all ___ and ___ phase species appear in the Kc expression
aqueous and gas
36
K = 1
doesn't favor reactants or products
37
K << 1 (much smaller than 1)
reverse rxn is favored
38
Q>>1 (much larger)
reaction has more products than reactants
39
the relationship between Kp and Kc
Kp = Kc (RT) ^n
40
heterogeneous equilibrium
reaction mixture that contains reactants and products that are in two or more different phases Pure solids and pure liquids DO NOT appear in the K expression equilibrium is independent of the amount of solid or liquid present as long as at least some is present in the reaction mixture
41
le Chatelier's principle
when a chemical system at equilibrium is disturbed, it returns to equilibrium by counteracting the disturbance disturbance causes a change in Q. reaction will shift to re-establish Q= K
42
ways equilibrium can be disturbed
1. adding or removing a reactant or product 2. changing the pressure 3. changing the temperature
43
adding or removing a pure liquid or solid:
has no effect on the system unless all the liquid or solid is removed
44
pressure changes will effect the equilibrium if:
the reaction contains gas phase species AND n is NOT equal to 0
45
exothermic reaction will shift
left
46
endothermic reaction will shift
right