Chemical Kinetics

Question 1

Which kind of reaction does a +ΔG indicate?

Answer 1

An endergonic reaction (energy is absorbed).

Reactants are higher in energy than products (ΔE= E_P-E_R= +).

Question 2

Which kind of reaction does a –ΔG indicate?

Answer 2

An exergonic reaction (energy is released.)

Products are lower in energy than reactants (ΔE= E_P-E_R= -).

Question 3

Is an exergonic reaction (–) spontaneous or nonspontaneous?

Answer 3

Spontaneous

ΔG < 0

Question 4

Is an endergonic reaction (+) spontaneous or nonspontaneous?

Answer 4

Nonspontaneous

ΔG > 0

Question 5

What is an intermediate?

Answer 5

A molecule that appears in the mechanism, but not the overall equation.

Question 6

What is the rate-determining step of a chemical reaction?

Answer 6

Slowest step

Question 7

In order for a reaction to occur between molecules, which three criteria must be met according to the Collision Theory?

The Collision Theory states that the rate of a reaction is proportional to the number of collisions per second between reacting molecules.

Answer 7

1. must collide
2. must collide with sufficient energy (enough to break bonds and form new bonds)
3. must have the correct orientation

Question 8

What is the Arrhenius equation?

Answer 8

Question 9

The Arrhenius equation shows the relationship between rate constant (k), and the temperature (T) of a reaction. According to this equation, which of the following will increase the rate of a reaction?

Answer 9

Temperature

The rate constant (k) is directly proportional to the rate of the reaction, and (k) increases with increasing temperature.

Question 10

What effect does temperature have on reaction rates?

Answer 10

Increased temperature = increased reaction rates

Question 11

For the Arrhenius equation, what increases the rate constant (k) and ultimately the reaction rate?

Answer 11

1. High temperature
2. Low E_a (activation energy)

Question 12

Once the transition state (activated complex) is formed, what happens to the reaction?

Answer 12

The reaction either proceeds towards products (forward) or towards reactants (backward).

(The transition state has GREATER energy than both the reactants and the products and is denoted by the symbol ‡).

Question 13

What are four main factors that affect reaction rates?

Answer 13

1. temperature (↑)
2. concentration of reactants (↑)
3. catalysts (lower E_A)
4. medium (polar solvents weaken bonds and increase reaction rates)

Question 14

For rate law k= [A]^x [B]^y, are the values of the exponents x and y, the same as the stoichiometric coefficients?

Answer 14

NO!

Unless it states that the reaction is elementary.

Question 15

Increasing the concentration of reactants will increase reaction rates for ALL reaction orders with the exception of?

Answer 15

Zero-order reactions

In an overall zero order reaction, it means that the reaction rate is independent of the concentration of any reactant. (rate = k[A]⁰[B]⁰ = k)

Question 16

Are reactants OR products excluded in rate law?

Answer 16

Products

Question 17

What are the only two factors that can change the rate of a zero-order reaction?

Answer 17

1. temperature
2. addition of a catalyst

Question 18

Which order reaction/kinetics does radioactive decay follow?

Answer 18

First-order reaction