Orders And Rate Equations

Question 1

What is the rate equation?

Answer 1

A + B–> C + D

Rate=k[A]^m[B]^n

*where m and n are the orders of reaction with respect to A and B

Question 2

What is k in the rate equation and what does it tell you? (3)

Answer 2

• Rate constant
• the bigger it is, the faster the reaction
• always the same for a certain reaction at a particular temperature

Question 3

What are the units for k?

Answer 3

Depends on the reaction

Question 4

What are the units for rate?

Answer 4

mol dm^-3 s^-1

Question 5

What does the order of a reaction tell you?

Answer 5

How the reactants concentration affects the rate

Question 6

What happens when the order of reaction to reactant “A” is 0 order?

Answer 6

• As A changes, rate of reaction remains the same

- e.g. If A doubles, triples etc, rate stays the same

Question 7

What happens when the order of reaction to reactant “A” is 1st order?

Answer 7

• Rate proportional to A

- As A doubles, rate of reaction doubles

Question 8

What happens when the order of reaction to reactant “A” is 2nd order?

Answer 8

• rate proportional to [A]^2

- i.e. If A doubles rate is 2^2=4 times faster

Question 9

How do you work our the overall order of a reaction?

Answer 9

Add the orders of the different reactants

Question 10

Can orders be worked out from chemical equations?

Answer 10

No only from experiments

Question 11

What are the methods for working out orders reaction with respect to A with experimental data? (3)

Answer 11

• use initial rates method and construct rate-concentration graph and examine shape
• use initial rates method to directly compare the intial rate for different concentrations of A
• continuously monitor change in conc of A against time and construct conc time graph then use graph to compare half lives

Question 12

What do you have to do to all the other reactants when working out orders?why? (2)

Answer 12

• Make sure they’re in excess

- This ensures change in rate is only due to A

Question 13

What does the order of a reaction tell you?

Answer 13

How the reactants concentration affects the rate

Question 14

What happens when the order of reaction to reactant “A” is 0 order?

Answer 14

• As A changes, rate of reaction remains the same

- e.g. If A doubles, triples etc, rate stays the same

Question 15

What happens when the order of reaction to reactant “A” is 1st order?

Answer 15

• Rate proportional to A

- As A doubles, rate of reaction doubles

Question 16

What happens when the order of reaction to reactant “A” is 2nd order?

Answer 16

• rate proportional to [A]^2

- i.e. If A doubles rate is 2^2=4 times faster

Question 17

How do you work our the overall order of a reaction?

Answer 17

Add the orders of the different reactants

Question 18

Can orders be worked out from chemical equations?

Answer 18

No only from experiments

Question 19

What are the methods for working out orders reaction with respect to A with experimental data? (3)

Answer 19

• use initial rates method and construct rate-concentration graph and examine shape
• use initial rates method to directly compare the intial rate for different concentrations of A
• continuously monitor change in conc of A against time and construct conc time graph then use graph to compare half lives

Question 20

What do you have to do to all the other reactants when working out orders?why? (2)

Answer 20

• Make sure they’re in excess

- This ensures change in rate is only due to A