Kinetics Flashcards

1
Q

Factors that Affect Reaction Rates

A

Physical state of reactants (increase surface area=increase # collisions)
Concentration of reactants (increase reactant=increase # collisions)
Temperature (increase temperature=increase KE=increase in # collisions and energy of collisions
Presence of a catalyst (decrease activation energy=require less energy for collisions)

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2
Q

Rate of appearence

A

change (B)/ Change (time) or -rate of disappearance of A

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3
Q

Rate of disappearance

A

change (A)/ Change (time)

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4
Q

Average Rate

A

Change in concentration over a specific time interval

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5
Q

Instantaneous Rate

A

Rate at a particular moment during the reaction

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6
Q

Initial Rate

A

Instantaneous rate at t=0

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7
Q

Rate Expression

A

Compares the rate of reactants and products relative to each other and relative to the overall rate of the reaction

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8
Q

Rate Law

A

Shows that rate depends on the concentration of reactants

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9
Q

Rate=

A

k A^m B^n
k= rate constant
m, n: reaction orders

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10
Q

Rate constant, k, depends on…

A

Temperature and a catalyst

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11
Q

Overall reaction orders =

A

m + n

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12
Q

Units of rate constant, k, depends on…

A

reaction order

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13
Q

Units of Rate Constant Chart

A

Units of Rate Constant Chart

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14
Q

Rate constant, k, does not depend on

A

Concentration

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15
Q

Plots of the Different Orders

A

Zero order-concentration vs. time
First order-ln concentration vs. time
Second order-1/concentration vs. time

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16
Q

Zero Order

A

Rate is independent of concentration
slope=-k
Rate Law: rate=k
Integrated Rate Law: [At]=-kt+[A0]
Half Life: t1/2=[A0]/2k

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17
Q

First Order

A

Rate depends on concentration of a single reactant
slope=-k
Rate Law: rate=k[A]
Integrated Rate Law: ln[At]=-kt+ln[A0}
Half Life: t1/2=0.693/k

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18
Q

Second Order

A

Rate depends on the concentration of [A^2] or [A] and [B]
slope=k
Rate Law: rate=k[A^2]
Integrated Rate Law: 1/[At]=kt + 1/[A0]
Half Life: t1/2= 1/k[A0]

19
Q

Half Life

A

Time required for reactant to reach 1/2 initial value
In zero and second order, the half-life depends on the initial concentration
First order is constant

20
Q

Elementary Reaction

A

A process in a chemical reaction that occurs in a single event or step
Can use stoichiometry to find rate law
Can involve simultaneous collision of three or more particles but rare
Elementary steps of a multistep mechanism adds up to overall chemical equation

21
Q

To find rate law for an overall reaction

A

you must use experimental data

22
Q

Reaction Mechanism

A

The process by which a reaction occurs

23
Q

The Collision Model

A

Molecules must collide in order to react
Increase # collisions = increase rate

24
Q

The Orientation Factor

A

Collisions must occur with molecules in the proper orientation for a reaction to occur

25
Activation Energy
Minimum energy to start reaction
26
Collision Theory
Collide, have proper orientation, have suffient energy
27
Change in energy does not relate to...
reaction rate
28
Endothermic vs. Exothermic
Endothermic=energy is absorbed so products have greater energy than reactants Exothermic=energy is given off so products have less energy than reactants
29
The Arrhenius Equation
k=Ae^-Ea/RT A: frequency factor, related to collisions and orientation R: 8.314 j/molK
30
Increase in temp or decrease in Ea will lead to...
increase rate constant
31
Molecularity
of molecules that are reactants Unimolecular= 1 molecule involved
32
Intermediate
A substance that is formed in on elementary step but used in a later one so it doesn't show in the overall reaction
33
Catalyst
A substance that speeds up a chemical reaction; it is present at the start of reaction and re-foremed in a later step but does not show up in overall reaction
34
How do you know that you are dealing with an elementary step?
It is a single step in a multi step mechanism or it tells you
35
Which steps determines the rate of the overall mechanism?
Slowest step limits the overrallr eaction
36
Mechanisms with a Slow Initial Step
Use coefficients from the slow step to get the rate law
37
Mechanisms with Fast Initial Step
Write rate law for the last step Write forward and backward rate law for the first step Substitute for the compound backing up the reaction
38
Peaks
Transition State/Elementary Steps
39
Valley
Intermediates
40
How do catalysts work?
They provide an alternate pathway with lower potential energy Leads to new reaction mechanism Leads to greater rate constant -Formation of a more stable activated complex, increase collision frequency, improves the orientation of the reactantants
41
Homogeneous Catalyst
In the same phase/state of matter as the reacting molecules
42
Heterogeneous Catalyst
In different phase/state of matter than the reacting molecules
43
Enzymes
Biological catalysts; usually proteins