Chapter 18 - Rates of Reaction

Question 1

What is rate of reaction equation?

Answer 1

Rate = change in concentration ÷ time

Question 2

Units of rate of reaction?

Answer 2

Mol dm^-3 s^-1

Question 3

What is rate of reaction proportional to?

Answer 3

[A]ⁿ where n = order

Question 4

Effect of concentration when zero order in respect to reactant?

Answer 4

Concentration of reactant has NO EFFECT on rate
Rate ∝ [A]⁰

Question 5

Effect on concentration when first order in respect to reactant?

Answer 5

Rate ∝ [A]¹

E.g. if concentration doubles then rate doubles

Question 6

Effect on concentration when second order in respect to reactant?

Answer 6

Rate ∝ [A]²

E.g. if concentration doubles rate quadruples

Question 7

What is the rate equation?

Answer 7

Rate = k x [A]^m [B]ⁿ

Question 8

What is the overall order of reaction?

Answer 8

Sum of orders with respect to each reactant e.g. m + n

Question 9

Which order is normally omitted when writing rate equation?

Answer 9

Zero order reactants
First order powers

Question 10

Methods of continuous monitoring for gas product?

Answer 10

• Gas collection
• Mass loss

Question 11

When can rate be monitored using a colorimeter?

Answer 11

When there is a coloured solution or precipitate

Question 12

Gradient of concentration-time graph is _____________

Answer 12

Rate of reaction

Question 13

Describe graph of zero order on a concentration-time graph?

Answer 13

Straight line with negative gradient
Gradient = rate constant (k)

Question 14

First order on a concentration-time graph has a constant __________

Answer 14

Half life

Question 15

What is half life?

Answer 15

Time taken for concentration of reactant to decrease to half its original value

Question 16

How to calculate rate constant from rate on a first order conc-time graph?

Answer 16

• Tangent to curve at particular concentration (gradient is rate)
• Use rate equation to calculate k

Question 17

How to calculate rate constant from half life on a first order conc-time graph?

Answer 17

k = ln2 ÷ t_1/2
where t_1/2 = half life

Question 18

What is the rate constant (k) on zero order rate-conc graph?

Answer 18

y intercept

Question 19

What is the rate constant (k) on first order rate-conc graph?

Answer 19

Gradient

Question 20

How to find initial rate using graph?

Answer 20

Draw tangent on concentration-time graph at t = 0 and find gradient

Question 21

How to find initial rate using clock reaction?

Answer 21

Time taken for a colour change where initial rate ∝ 1/t

Question 22

The slowest step in the multi step reaction is the _______________

Answer 22

Rate determining step

Question 23

The rate equation must only include the reacting species involved in the __________

Answer 23

Rate determining step

Question 24

The _______ in the rate equation must match the number of species involved in the ______________

Answer 24

• Orders
• Rate determining step

Question 25

The fast and slow step must combine to form the ____________

Answer 25

Overall equation

Question 26

What happens to rate constant (k) when temperature increases?

Answer 26

Rate increases so value of k increases

Question 27

What is Arrhenius’ equation?

Answer 27

k = Ae^-Ea/RT

Question 28

What is the logarithmic form of Arrhenius’ equation?

Answer 28

lnk = (-E_a / RT) + lnA

Question 29

How to calculate A from graph of lnk against 1/T?

Answer 29

The y intercept is lnA
So A = e^lnA

Question 30

How to calculate E_a from graph of lnk against 1/T?

Answer 30

Gradient = -E_a / R
So E_a = 8.314 x (+) gradient = energy in J so ÷ 1000 to get in kJ