HIGHER CHEMISTRY REVISION.
Unit 1:- Reaction Rates
1.
A student was asked to write a plan of the procedure for an investigation.
The entry made in her laboratory notebook is shown below.
(a) This method does not
keep the overall volume
of the reaction
mixture constant.
(b)
Do not use 1
measuring cylinder
to measure out all
the solutions. Use
separate ones with
the size related to
the volumes of
solutions used.
Start timing as soon
as the hydrogen
peroxide is added to
the other reactants.
(a)
Why is instruction 4 not the best way of altering the concentration of
the potassium iodide solution?
(b)
State two other ways of improving the student’s plan of this
investigation procedure.
2.
The balanced equation for the decomposition of hydrogen peroxide into
water and oxygen is:
2H2O2 (l)

2H2O(l) + O2 (g)
The following graph is obtained for the volume of oxygen released over time.
Calculate the average rate of reaction between 10 s and 20 s.
Rate = 40-24/20
= 0.8 cm3 s-1.
3. The decomposition of hydrogen peroxide solution into water and oxygen can be catalysed by an enzyme.
2H2O2 (l)

2H2O(l)
+
O2 (g)
The rate of reaction can be followed by recording the mass loss over a period of time.
(a) The following graph was obtained from experiments to find the effect of pH on the
efficiency of the enzyme.
(a) (i) rate =
(60.01)-(59.68)/
20
= 0.165g min-1.
(ii) The enzyme is most
efficient between a
pH of 7 and 10.
(b) The rate could be measured
by collecting the oxygen gas
in a gas syringe and plotting
the volume of gas collected
against time.
(i) Calculate the average rate of the reaction over the first 20 minutes,
in g min-1, for the experiment at pH 10.
(ii) From the results shown on the graph, what can be concluded about the
efficiency of the enzyme over the pH range used in the experiment?
(b) Give one other way of following the rate of this reaction
4. The grid shows the possible effect of temperature change on reaction rate.
A
B
E
D
C
F
Identify the graph which shows how the rate of reaction varies with
temperature in the decomposition of hydrogen peroxide solution using
catalase, an enzyme, found in potatoes.
Graph in box D.
5. The effect of temperature changes on reaction rate can be studied using the
reaction between an organic acid solution and acidified potassium permanganate
solution.
5(COOH)2(aq) + 6H+(aq) + 2MnO4-(aq)

2Mn2+(aq) + 10CO2(g) + 8H2O(l)
The apparatus required is shown in the diagram.
(a) Name the organic acid.
(b) Describe how the reaction time can be measured.
(c) The headings for a set of results are shown below.
Temperature of reaction /°C
Reaction time /s
Reaction rate /
Complete the headings by entering the correct unit in the third column.
(a)
Oxalic acid.
(b)
Start timing when solutions are mixed and stop timing when purple colour
appears.
(c)
s-1.
6. Methanoic acid, HCOOH, can break down to carbon monoxide and water by two
different reactions, A and B.
Reaction A (catalysed)
HCOOH(aq)
+ H+(aq)  CO(g)
+ H2O(l)
+ H+ (aq)
Reaction B (uncatalysed)
HCOOH(aq)

CO(g)
+ H2O(l)
(a) (i) What is the evidence in the equation for Reaction A that the H +(aq) ion
acts as a catalyst?
(ii) Explain whether reaction A is an example of heterogeneous or homogeneous
catalysis.
( b) The energy diagram for the catalysed reaction is:-
(a) (i) Hydrogen ions are
not used up in the
reaction.
(ii) Homogeneous – the
catalyst and reactant
are in the same
physical state.
(b) The uncatalysed
reaction has a higher
activation energy.
Copy the diagram and draw a line to show the reaction pathway for the
uncatalysed reaction.
7. The effect of temperature on reaction rate can be studied using the reaction
between oxalic acid and acidified potassium permanganate solution.
(a) What colour change would indicate that the reaction was complete?
(b) A students results are shown in the graph below.
(
(a) The appearance of a
purple colour.
(i) Use the graph to calculate the reaction time, in s, at 40oC.
(b) (i) Rate = 0.12
Time =
1/
0.12
= 8.33 s
(ii) Rate is very slow at
room temperature.
(ii) Why is it difficult to obtain an accurate titration time when the reaction is
carried out at room temperature
8. The diagram below shows the energy distribution of molecules in a gas at a
particular temperature.
EA
Draw a second curve on the diagram to show the energy distribution of the
molecules in the gas at a higher temperature.
Label the diagram to indicate why an increase in temperature has such a
significant effect on reaction rate.
The second curve (blue line) shows that the average kinetic energy
of the molecules has increases. The orange line shows the
activation energy (EA) for the reaction. The increase in
temperature has greatly increased the number of molecules that
possess the activation energy.