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Chem 105 > Unit 1: Reaction Kinetics > Flashcards

Unit 1: Reaction Kinetics Flashcards

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1
Q

What is Rate of Reaction?

A

The change in concentration of a species over an interval of time.

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2
Q

How are the rates of formation and disappearance measured?

A

Experimentally, therefore they do not include stoichiometric coefficients.

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3
Q

Rates of formation and disappearance are always equal to the rate of reaction.

A

False, they are not necessarily equal.

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4
Q

The Rate of Reaction is always positive.

A

True, rates of disappearance are negative.

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5
Q

Are rates of formation and disappearance the same amongst different species?

A

No, they are not the same.

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6
Q

What is Instantaneous rate of reaction?

A

The change in concentration of a species at a specific time.

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7
Q

What is one way the rate of reaction can be determined?

A

By dividing the rates of formation and disappearance by their respective coefficients.

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8
Q

Reaction rates are dependent on concentration.

A

True, but the rate constant and order of the reaction are independent.

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9
Q

How is the order of a rate law equation determined?

A

Experimentally by looking at inital rates of rxn at differing concentrations and then by taking the sum of n and m.

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10
Q

What is a rate law?

A

It defines how the rate of a reaction depends on a species.

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11
Q

What does the rate constant depend on?

A

The reaction and temperature (larger k = faster reaction).

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12
Q

When looking at initial rates you should account for every species that is monitored.

A

True, products can be monitored and eventually appear in the rate law expression.

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13
Q

What is the rate law of a zero order reaction?

A

rate = k

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14
Q

In a zero order reaction what is the units for k?

A

M/s

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15
Q

In a zero order reaction what is the equation for half-life?

A

[A]0/2k

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16
Q

In a zero order reaction what is the integrated rate law?

A

[A]t = -k*t + [A]0

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17
Q

What is the graph of a zero order reaction? Is the slope + or -?

A

[A]t vs. t and the slope is negative

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18
Q

What is the rate law of a first order reaction?

A

rate = k[A]

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19
Q

In a first order reaction what are the units for k?

A

1/s

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20
Q

In a first order reaction what is the equation for half-life?

A

ln2/k

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21
Q

In a first order reaction what is the integrated rate law?

A

ln[A]t = -k*t + ln[A]0

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22
Q

What is the graph of a first order reaction? Is the slope + or -?

A

ln[A]t vs t and the slope is negative

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23
Q

What is the rate law of a second order reaction?

A

rate = k[A]^2

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24
Q

In a second order reaction what are the units for k?

A

1/Ms

25
Q

In a second order reaction what is the equation for half-life?

A

1/k[A]0

26
Q

In a second order reaction what is the integrated rate law?

A

1/[A]t = k*t + 1/[A]0

27
Q

What is the graph of a second order reaction? Is the slope + or -?

A

1/[A]t vs t and the slope is positive

28
Q

What order of reaction is radio active decay?

A

First order

29
Q

Surface reactions and many enzyme-catalyzed reactions follow zero order reaction kinetics?

A

True

30
Q

What is the Arrhenius equation?

A

k = Ae^(-Ea/RT)

31
Q

What is A and Ea in the equation?

A

A = frequency factor (pre-exponential factor) and Ea = activation energy

32
Q

What is the exponential factor?

A

The fraction of molecules with enough/sufficient energy to react. It is a # between 0 and 1.

33
Q

What is the exponential factor equation?

A

f = e^(-Ea/RT)

34
Q

What happens with a low Ea and high T?

A

The exponential factor approaches 1.

35
Q

What happens with a high Ea and low T?

A

The exponential factor becomes small, it approaches 0.

36
Q

What is the frequency factor?

A

The # of times the reactants approach the activation barrier per unit time.

37
Q

What is the linearized Arrhenius equation?

A

lnk = -Ea/R * 1/T +lnA

38
Q

What is the collision theory?

A

A reaction occurs after a sufficiently energetic collision between two reactant molecules.

39
Q

What is needed for a collision to be effective?

A

Ea has to be met and the molecules need to be properly orientated.

40
Q

With collision theory what is the rate constant?

A

k = pZf , where p = steric (orientation factor) and Z = # of collisions per unit volume

41
Q

What is the transition state model?

A

It describes how reactants become products assuming favorable collisions occur. It focuses on the change of kinetic energy to potential energy as particles collide.

42
Q

What happens during collisions?

A

-Bonds in the reactants stretch and become weaker.
-New intermolecular bonds start to form (still weak at this stage).
-The transition species is known as the transition state (activation complex).

43
Q

If E reactants > E products the reaction is?

A

Exothermic

44
Q

If E reactants < E products the reaction is?

A

Endothermic

45
Q

What are the characteristics of the transition state?

A

-High energy
-Short-lived (unstable)
-Exact structure is unknown
-In equilibrium (low concentrations) with reactants and products

46
Q

What is reaction mechanisms?

A

The theoretical concept that describes how a reaction occurs through a series of elementary reactions.

It MUST be consistent with the overall stoichiometry of the reaction AND account for the experimentally determined rate law.

47
Q

What can the mechanism involve?

A

-Several steps
-Intermediate species

48
Q

What are intermediate species?

A

A species that appears as a product in one step and then is consumed in another.

49
Q

What is molecularity?

A

The # of species that must collide simultaneously.

It CANNOT be fractional or negative.

50
Q

Elementary rate law?

A

rate = k[species]^n , where n is the stoichiometric coefficient.

51
Q

What are the 4 types of mechanisms?

A
  1. Slow step followed by fast step(s)
  2. Fast step(s) followed by a slow step
  3. Steady state (approximation)
  4. Too complex
52
Q

What is the rate-determining step

A

The slowest step

53
Q

Does each step in a mechanism have its own transition state?

A

Yes

54
Q

What is a catalyst?

A

A substance that increases the rate but is not consumed in the overall reaction.

55
Q

What does a catalyst do?

A

-Decreases Ea
-No influence on enthalpy
-No influence on the amount of product
-It allows equilibrium to be reached faster (k is not changed)

56
Q

What is a Homogeneous Catalyst?

A

The catalyst is the same phase as the reactant.

57
Q

What is a Heterogeneous Catalyst?

A

The catalyst is a different phase as the reactant, often it is solid.

The reactant(s) adsorb onto the solid surface, which weakens the bonds.

58
Q

What is an example of a heterogeneous catalyst?

A

Hydrogenation, which means adding hydrogen.

Chem 105 (5 decks)

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