exam questions

Question 1

explain why an excess of a reactant may be used (2)

Answer 1

• the concentration remains constant
• it will be zero order

Question 2

how would you show that a reaction is first order using a graph? (2)

Answer 2

• draw two half lives
• half life will be constant

Question 3

how would you determine the initial rate of reaction on a rate time graph? (2)

Answer 3

• draw a tangent at T=0
• change in y / change in x

Question 4

how can orders be worked out from a set of results? (3)

Answer 4

• first order = concentration and rate increase proportionally
• zero order = concentration has no effect on rate
• second order = concentration changes rate proportionally squared

Question 5

what order does a negative linear concentration time graph show? (1)

Answer 5

zero

Question 6

what order does a positive linear rate time graph show?

Answer 6

first

Question 7

how is activation energy calculated from a graph? (2)

Answer 7

• change in y / change in x
• x 8.314

Question 8

what part of arrhenius is represented by y? (1)

Answer 8

lnk

Question 9

what part of arrhenius is represented by m? (1)

Answer 9

-Ea / R
(gradient)

Question 10

what part of arrhenius is represented by x? (1)

Answer 10

1/T

Question 11

what part of arrhenius is represented by c? (1)

Answer 11

lnA
(y intercept)

Question 12

how is A calculated from an lnk 1/T graph? (2)

Answer 12

• identify where line of best fit crosses y axis
• inverse log (e power) this value

Question 13

what are the units for Ea in the arrhenius equation? (1)

Answer 13

J mol -1

Question 14

what experimental methods allows rate of reaction to be measured over time? (2)

Answer 14

• measuring mass loss
• measuring volume of gas produced

Question 14

how is J mol -1 converted to kjmol-1? (1)

Answer 14

x 1000

Question 15

what apparatus would allow gas volume to be collected? (1)

Answer 15

gas syringe

Question 16

describe a catalyst in a multi step mechanism (2)

Answer 16

• used and reformed
• only in overall equation, not rate equation

Question 17

state what is meant by rate determining step (1)

Answer 17

slowest step in multi step mechanism

Question 18

how would you find k from a rate concentration graph?
(rate equation given) (3)

Answer 18

• rearrange rate equation
• sub rate and concentration in at the same point
• units

Question 19

suggest 2 reasons why it is unlikely that a reaction could take place in one step (2)

Answer 19

• rate equation does not match whole equation stoichiometry
• collision unlikely with more than 2 species