Rate equations

Question 1

What is the reaction rate?

Answer 1

It is the change in concentration of a reactant or product per unit time.

Question 2

What is the gradient of a concentration against time graph?

Answer 2

Reaction rate

Question 3

What is an order of reaction?

Answer 3

It is defined as the power to which the concentration of its reactant is raised in the rate equation

Question 4

What is the order of reaction of [A] when it is changed but the rate is constant?

Answer 4

[A] has zero order

Question 5

What is the order of reaction of [A] when the rate is proportional to [A]?

Answer 5

[A] has first order

Question 6

What is the order of reaction of [A] when the rate is proportional to [A]^2?

Answer 6

[A] has second order

Question 7

What is the overall order of a reaction?

Answer 7

It is the sum of the powers of the concentrations in the rate equation

Question 8

How can orders of reaction be found?

Answer 8

They can ONLY be found by EXPERIMENT at a CONSTANT temperature

Question 9

How does temperature affect the rate constant(k)?

Answer 9

When the temperature is increased, the rate of reaction increases. The concentrations and orders of reaction are constant. Therefore, k increases for the rate equation to balance.

Question 10

What is the initial rate of a reaction?

Answer 10

It is the rate right at the start of the reaction when t=0s.

Question 11

What can be done to calculate orders of reaction?

Answer 11

• Set up a series of experiments
• Change a single substance’s concentration
• See what happens to the initial rate

Question 12

What are the different ways that the rate of a reaction be calculated?

Answer 12

Measure gas volume
Measure loss of mass
Observe colour change
Change in pH

Question 13

What is the rate determining step?

Answer 13

Itis the slowest step in a multi-step reactio nand determines the overall rate of the reaction

Question 14

How can you which reactant must in the rate determining step?

Answer 14

If the reactant appears in the rate equation, it affects the rate. Therefore, the reactant or something derived from it must be in the rate determining step.

Question 15

What are the key points to remember about the rate determining steps and mechanisms?

Answer 15

The rate determining step doesn’t have to be the first step in a mechanism
The reaction mechanism can’t usually be predicted from just the chemical equation

Question 16

Why does the rate-determining step determine the overall rate of the reaction?

Answer 16

This step requires the most energy and has the highest activation energy

Question 17

What is the Arrhenius Equation?

Answer 17

It shows how the rate constant varies with temperature and activation energy

k=Ae^(-activation energy/RT)

Question 18

How is k affected when the activation energy increases?

Answer 18

k decreases

Slower rate with fewer successful collisions due to a higher activation energy

Question 19

How is k affected when the temperature increases?

Answer 19

k increases

Faster rate with an increased number of successful collisions, as more particles have at least the activation energy