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CHEM 115 > Chapter 13 - Chemical Kinetics > Flashcards

Chapter 13 - Chemical Kinetics Flashcards

1
Q

What is chemical kinetics?

A

Study of rate of change of concentrations of substances involved in chemical reactions

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2
Q

Define reaction rate.

A

How rapidly a reaction occurs

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3
Q

List factors affecting reaction rates.

A
  • Physical state of reactants
  • Concentration of reactants
  • Temperature
  • Presence of a catalyst
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4
Q

What is the relationship between reaction rate and stoichiometry?

A

Relative rates of consumption of reactants and formation of products based on stoichiometry

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5
Q

What is the average rate of a reaction?

A

Change in concentration of reactant or product over a specific time interval

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6
Q

How is the instantaneous reaction rate determined?

A

Determined graphically as tangential slope of concentration versus time plot

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7
Q

What is the rate law?

A

Equation that defines the experimentally determined relationship between reactant concentrations and the rate of the reaction

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8
Q

Define reaction order.

A

Experimentally determined number defining the dependence of the reaction rate on the concentration of a reactant

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9
Q

What is the rate constant (k)?

A

Proportionality constant that relates the rate of a reaction to the concentration of reactants

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10
Q

What is the overall order of reaction?

A

Sum of exponents of concentration terms in the rate law

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11
Q

What happens in a first-order reaction when the concentration is doubled?

A

The rate changes by the same factor

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12
Q

In a second-order reaction, what happens to the initial rate when the reactant concentration is doubled?

A

The initial rate quadruples

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13
Q

What does a zero-order reaction indicate about the concentration of A?

A

The rate is independent of the concentration of A

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14
Q

What is the half-life (t1/2) of a first-order reaction?

A

The time during which the concentration of a reactant decreases by half

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15
Q

True or False: The half-life of a first-order reaction is dependent on the initial concentration.

A

False

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16
Q

What is the Arrhenius equation?

A

k = Ae^(-Ea/RT)

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17
Q

What does the frequency factor (A) in the Arrhenius equation represent?

A

The number of times the reactants approach the activation barrier per unit time

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18
Q

What is an activated complex?

A

A temporary, high energy (unstable) chemical species formed during a reaction

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19
Q

Define reaction mechanism.

A

A series of small reactions involving 1, 2, or at most 3 molecules that lead to the overall observed reaction

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20
Q

What is the rate determining step (RDS)?

A

The slowest step in a reaction mechanism that determines the rate of the overall reaction

21
Q

What is molecularity in the context of elementary steps?

A

The number of reactant particles in an elementary step

22
Q

What is the orientation factor (p) in the collision model?

A

The probability that colliding molecules are aligned properly for reaction

23
Q

What does Svante Arrhenius’s rule state regarding temperature and reaction rates?

A

For each 10°C rise in temperature, the speed of the reaction doubles

24
Q

Fill in the blank: The half-life of a zero-order reaction depends on the _______.

A

[initial concentration]

25
What is the significance of the slope in a first-order reaction graph of ln[A] vs. time?
The slope equals -k
26
True or False: The half-life of a second-order reaction is independent of the initial concentration.
False
27
What is the dependency of the rate constant (k) on temperature?
Changing the temperature changes the rate constant of the rate law
28
What is a reaction intermediate?
A species produced in one step of a reaction and consumed in a subsequent step
29
What is the effect of increasing temperature on reaction rate?
Increases reaction rate
30
What is activation energy?
The minimum energy required to initiate a chemical reaction.
31
What is the first step in a reaction mechanism called?
Rate determining step (RDS).
32
How does the rate law of the first step relate to the overall reaction?
The rate law of the first step is the same as the rate law of the overall reaction.
33
What are the two conditions to validate a reaction mechanism?
* The elementary steps must sum up to the overall reaction * The predicted rate law must be consistent with the experimentally observed rate law.
34
What is the predicted rate law for the reaction NO2(g) + CO(g) → NO(g) + CO2(g)?
Ratepredicted = k[NO2]2.
35
What is the overall reaction when the proposed mechanism includes NO2(g) + NO2(g) → NO3(g) + NO(g)?
NO2(g) + CO(g) → NO(g) + CO2(g).
36
What is the rate of the slow step in the proposed mechanism?
Rate = k1[NO2]2.
37
What occurs in a mechanism with a fast initial step?
The rate limiting step may contain intermediates.
38
What happens when a previous step in a mechanism is rapid and reaches equilibrium?
The forward and reverse reaction rates are equal.
39
What is an intermediate in a reaction mechanism?
A product of a fast step that is consumed in a subsequent step.
40
What is the experimentally determined rate law for the reaction 2 H2(g) + 2 NO(g) → 2 H2O(g) + N2(g)?
Rate = k [H2][NO]2.
41
What is the role of a catalyst in a chemical reaction?
To increase the reaction rate without being consumed.
42
What are positive catalysts and negative catalysts?
* Positive catalysts speed up a reaction * Negative catalysts or inhibitors slow down a reaction.
43
What are the two types of catalysis based on phase?
* Homogeneous: same phase as reactants * Heterogeneous: different phase than reactants.
44
In homogeneous catalysis, what is an example of a catalyst?
Cl(g) in the destruction of O3(g).
45
In heterogeneous catalysis, what is an example of a catalyst?
Solid catalytic converter in a car’s exhaust system.
46
What are enzymes?
Protein molecules that catalyze biological reactions.
47
How do enzymes work?
By adsorbing the substrate onto an active site that orients it for effective reaction.
48
Fill in the blank: Catalysts are substances that affect the rate of a reaction without being ______.
consumed.
49
By what factor would you expect the reaction rate to increase if a catalyst lowers the activation barrier from 123 kJ/mol to 58.0 kJ/mol?
This requires calculations based on the Arrhenius equation.

CHEM 115 (1 decks)

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