A2- Rate Equations

Question 1

Draw the graph showing concentration-time for a 0 order reaction

Answer 1

straight line sloping downwards
x axis= time
y axis= concentration
https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1920,f=auto/uploads/2021/01/5.6-Reaction-Kinetics-Zero-Order-Concentration.png

Question 2

Draw the graph showing concentration-time for a 1st order reaction

Answer 2

curved line sloping down wards,with a constant half life
(less steep than 2nd initially)
x axis= time
y axis= concentration

Question 3

Draw the graph showing concentration-time for a 2nd order reaction

Answer 3

curved line sloping downwards
(more steep than 1st)
x axis= time
y axis= concentration

Question 4

Draw the graph showing rate-concentration for a 0 order reaction

Answer 4

horizontal line
x axis= concentration
y axis= rate

https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1920,f=auto/uploads/2021/01/5.6-Reaction-Kinetics-Zero-Order-Rate.png

Question 5

Draw the graph showing rate-concentration for a 1st order reaction

Answer 5

straight line sloping upwards
x axis= concentration
y axis= rate

https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1920,f=auto/uploads/2021/01/5.6-Reaction-Kinetics-First-Order-Rate.png

Question 6

Draw the graph showing rate-concentration for a 2nd order reaction

Answer 6

curved line sloping up
gets steeper as concentration increases
x axis= concentration
y axis= rate

Question 7

How do you work out the total order of a reaction?

Answer 7

add up the order of each reactant

Question 8

If the reaction is 1st order with respect to reactant A, describe the relationship between rate and concentration of A

Answer 8

rate is directly proportional to [A]
(will change by same multiple)

Question 9

If the reaction is 2nd order with respect to reactant A, describe the relationship between rate and concentration of A

Answer 9

rate is directly proportional to [A]^2
(will change by multiple^2)

Question 10

If the reaction is 0 order with respect to reactant A, describe the relationship between rate and concentration of A

Answer 10

rate is directly proportional to [A]^0
(there would be no change)

Question 11

How would you rearrange a rate equation to find k?

Answer 11

k= rate/[A]^x[B]^y

Question 12

How would a conc-time graph show a reactant is first order?

Answer 12

if it has got a constant half life

Question 13

What are the units for activation energy in the arrhenius equation?

Answer 13

give in kJ but need to be converted into J

Question 14

What is the inverse version of the Arrhenius equation?

Answer 14

lnk = -Ea/R * 1/T - lnA

Question 15

How would we work out the activation energy using a graph?

Answer 15

work out gradient (change in y/change in x)
m = -Ea/R
so m*R = -Ea

Question 16

What is the significance of a zero order reactant in the mechanism of a reaction?

Answer 16

does not appear in the rate determining step

Question 17

How would you identify a catalyst?

Answer 17

• reactant in step 1, product in the other
• can be in the rate expression
• will not be in overall equation

Question 18

How would you identify an intermediate?

Answer 18

• product in 1st step, then used up as a reactant
• cannot be in the rate equation
• will not be in overall equation

Question 19

What is the arrhenius equation?

Answer 19

k = Ae^(-Ea/RT)

Question 20

How would a conc-time graph show a reactant is 0 order?

Answer 20

has a constant gradient

Question 21

Why does a large excess of other reactants mean the rate is only impacted by the other reactant (which is not in excess)?

Answer 21

• concentrations are effectively constant (any change is negligible)
• so have a constant/no effect on the rate