The Rate Law and Its Components

Question 1

For a reaction at a fixed temperature
aA + bB … –> cC + dD …, what is the Rate Law?

Answer 1

Rate = k[A]^m [B]^n …

Question 2

In the rate law, what is k?

Answer 2

The rate constant, which relates reaction rate to reactant (and product concentrations). It is specific for a given reaction at a given temperature

Question 3

In the rate law, what are m and n?

Answer 3

Reaction orders

Question 4

What do reaction orders define?

Answer 4

How a reaction rate is affected by reactant concentrations

Question 5

What differs between the rate law and the general expression of rate?

Answer 5

The rate law also tells how reaction rate changes with concentration.

Question 6

Is reaction rate proportional to concentration?

Answer 6

Not always

Question 7

Does reaction order refer to each reactant or the overall reaction?

Answer 7

Both. There are reaction orders of reactants and of the overall reaction

Question 8

How do you find the overall reaction order?

Answer 8

Add the reaction orders of individual reactants

Question 9

If the reaction order is zero with respect to [A], what happens to the rate when [A] doubles?

Answer 9

The rate does not change. Zero order means rate is independent of concentration

Question 10

If the reaction is 1st order with respect to [A], what happens to the rate when [A] doubles?

Answer 10

The rate doubles

Question 11

If the reaction is 2nd order with respect to [A], what happens to the rate when [A] doubles?

Answer 11

The rate quadruples

Question 12

If a reaction is 1/2 order with respect to [A], what happens to the rate when [A] quadruples?

Answer 12

The rate doubles

Question 13

If a reaction is -1st order with respect to [A], what happens to the rate when [A] doubles?

Answer 13

The rate is half as fast

Question 14

Can you determine reaction orders from a balanced chemical equation?

Answer 14

No, they are determined by experimentation

Question 15

Rate = k[A]^2
What is the reaction order?

Answer 15

2nd order

Question 16

Rate = k
What is the reaction order?

Answer 16

Zero order

Question 17

Rate = k[A][B]
What is the overall reaction order?

Answer 17

2nd order

Question 18

Rate = k[A]
What is the overall reaction order?

Answer 18

1st order

Question 19

Rate = k[A][B]^2
What is the overall reaction order?

Answer 19

Third order

Question 20

What is a negative reaction order?

Answer 20

When the rate decreases as the concentration of a component increases.

Question 21

If rate = k[A]^2, by what factor does the rate change if [A] is tripled?

Answer 21

By a factor of 9 (3^2 = 9)

Question 22

If rate = k[A]^2 [B], by what factor does the rate change if both [A] and [B] are doubled?

Answer 22

By a factor of 8
Rate = k(2^2)(2) = k(4)(2) = 8k

Question 23

What is the general formula for units of k?

Answer 23

[(L/mol)^(overall order - 1)] / (unit of t)

Question 24

What are the units of k for a zero order reaction?

Answer 24

mol/L⋅s

Question 25

What are the units of k for a first order reaction?

Answer 25

1/s or s^-1

Question 26

What are the units of k for a second order reaction?

Answer 26

L/mol⋅s

Question 27

What are the units of k for a third order reaction?

Answer 27

L^2/(mol^2 ⋅ s)

Question 28

For rate = k[A]^2, if [A] is halved, by what factor is the initial rate changed?

Answer 28

The rate would be 1/4 of the initial rate
(1/2)^2 = 1/4