Changing the temperature
3 marks · NormalA reversible reaction is shown below.
Calculate the enthalpy change (ΔH) for the reverse reaction. State whether the reverse reaction is exothermic or endothermic.
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\Delta H = -75\ \text{kJ/mol}. The reverse reaction is exothermic. kJ/mol (±0)
Also accept: -75 kJ/mol, exothermic
Common mistakes: Not changing the sign of ΔH; Saying reverse is endothermic
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Marking points
M1 · 1 mark · States that ΔH for the reverse reaction is the negative of forward ΔH.
A1 · 1 mark · Correct value: −75 kJ/mol.
B1 · 1 mark · States the reverse reaction is exothermic.
Worked solution
For the reverse reaction, the sign of ΔH is changed.
A negative ΔH means exothermic, so the reverse reaction is exothermic.