Chapter 18

Question 1

The rate of reaction

Answer 1

change in concentration of a substance in unit time

Question 2

unit of rate

Answer 2

mol dm-3 s-1

Question 3

When a graph of concentration of reactant is plotted
time, the gradient

Answer 3

is the rate of reaction.

Question 4

initial rate

Answer 4

the rate at the start of the
reaction where it is fastest.

Question 5

Reaction rates can be calculated from (graph)

Answer 5

graphs of
concentration of reactants or products, by drawing a
tangent to the curve (at different times) and calculating
the gradient of the tangent.

Question 6

generalised rate equation is:

Answer 6

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

Question 7

r

Answer 7

rate

Question 8

m, n are called

Answer 8

reaction orders
Orders are usually integers 0,1,2

Question 9

k is called

Answer 9

the rate constant

Question 10

total order

Answer 10

is worked
out by adding all the individual orders
together (m+n)

Question 11

For zero order: the concentration of A

Answer 11

has no effect on the
rate of reaction r = k[A]0 = k

Question 12

For first order: the rate of reaction

Answer 12

is directly proportional
to the concentration of A r = k[A]1

Question 13

For second order: the rate of reaction

Answer 13

is proportional to the
concentration of A squared r = k[A]2

Question 14

For a rate concentration graph to show the order of a particular reactant the concentration must be… whilst others should be

Answer 14

the concentration of that reactant must be varied
whilst the concentrations of the other
reactants should be kept constant.

Question 15

Continuous rate data

Answer 15

This is data from one experiment where the concentration
of a substance is followed throughout the experiment.

Question 16

Continuous rate data is processed by plotting the data and calculating

Answer 16

successive half-lives.

Question 17

The half-life of a first-order reaction
is

Answer 17

independent of the concentration and is constant.

Question 18

If half-lives rapidly increase then

Answer 18

the order
is 2nd order.

Question 19

The units of k depend on

Answer 19

the overall order of
reaction. It must be worked out from the rate
equation

Question 20

The value of k is independent of

Answer 20

concentration and
time. It is constant at a fixed temperature.

Question 21

The value of k refers to a specific AND it increases if

Answer 21

temperature and
it increases if we increase temperature

Question 22

For a 1st order overall reaction the unit of k is

Answer 22

s^-1

Question 23

For a 2nd order overall reaction the unit of k is

Answer 23

mol-1 dm3 s-1

Question 24

For a 3rd order overall reaction the unit of k is

Answer 24

mol-2 dm6 s-1

Question 25

If conc is doubled and rate stays the same: (order)

Answer 25

order= 0

Question 26

If conc is doubled and rate doubles:

Answer 26

order= 1

Question 27

If conc is doubled and rate quadruples :

Answer 27

order= 2

Question 28

Working out orders when two reactant concentrations are changed simultaneously In a reaction where the rate equation is r = k [A] [B]2

Answer 28

If the [A] is x2 that rate would x2 If the [B] is x3 that rate would x32= x9 If these changes happened at the same time then the rate would x2x9= x 18

Question 29

Arrhenius equation

Answer 29

k=Ae^-EA/RT where A is a constant R is gas constant and EA is activation energy.

Question 30

The Arrhenius equation can be rearranged ln k =

Answer 30

constant – EA/(RT)

Question 31

EA = (On graph)

Answer 31

- gradient x R

Question 32

Gradient =

Answer 32

- EA/ R

Question 33

The slowest step is called

Answer 33

the rate-determining step.

Question 34

The molecularity (number of moles of each substance) of the molecules in the slowest step will be the same as

Answer 34

the order of reaction for each substance. e.g. 0 moles of A in slow step would mean A is zero order. 1 mole of A mean A is first order