# Buy Exothermic and Endothermic Reactions

Quick questions
1 The reaction between zinc and copper sulfate solution causes the
temperature of the solution to rise. Is the reaction exothermic or
endothermic?
2 Give one example of an application of an endothermic reaction.
3 Give one variable that would affect the temperature change when
hydrochloric acid reacts with magnesium metal.
4 Define the term ‘activation energy’.
5 State which quantity is greater for an endothermic reaction: the
amount of energy absorbed during bond breaking, or the amount
of energy released during bond making.
Exam-style questions
6 When ammonium nitrate, NH4NO3, is dissolved in water the
temperature of the solution formed decreases.
NH4NO3(s) water → NH4NO3(aq)
A student investigated how the mass of ammonium nitrate
dissolved affected the temperature change of the solution.
6–1 Write down whether the dissolving of ammonium nitrate is
6–2 Draw a fully labelled reaction profile for the dissolving of
ammonium nitrate to form a solution. [3]
6–3 Describe a method the student could use to investigate how
the mass of ammonium nitrate dissolved affects the change in
temperature of the water. Your method should give valid results. [6]
Total: 11
p231–2 5.5.1.1
p232 5.5.1.1
p233 5.5.1.2
p235–7 5.5.1.3 MS1a
p233 5.5.1.2
p234 5.5.1.1 RP4
AT1,3,
5,6
p234 5.5.1.1 RP4
AT1,3,
5,6
p232–3 5.5.1.1

Energy changes topic review
95
7 Hydrogen peroxide, H2O2, is a very useful compound. It is very
reactive due to the single covalent bond between the two oxygen
atoms. Hydrogen peroxide decomposes to form water and oxygen.
Figure 1 shows the displayed formulae for the decomposition of
hydrogen peroxide.
H
O
H H
O H
2 O 2 O O
Figure 1
Table 1 shows the bond energies and the overall energy change
for the decomposition of hydrogen peroxide. Calculate the bond
energy X for the O–O bond in hydrogen peroxide. Use Figure 1
and Table 1. [4]
H-O O-O O=O Overall energy change
Energy in kJ/mol 463 X 496 –208
Table 1
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