The enthalpy change of neutralisation of hydrochloric acid may be determined using the apparatus shown. The equation for the reaction is $$\[ \mathrm{HCl}(\mathrm{aq})+\mathrm{NaOH}(\mathrm{aq}) \rightarrow \mathrm{NaCl}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \]$$ Procedure Step 1 Place $$\(25.0 \mathrm{~cm}^{3}\)$$ of $$\(1.00 \mathrm{~mol} \mathrm{dm}^{-3}\)$$ hydrochloric acid in a polystyrene cup. Record the temperature of the hydrochloric acid. Step 2 Record the temperature of $$\(30.0 \mathrm{~cm}^{3}\)$$ of $$\(1.00 \mathrm{~mol} \mathrm{dm}^{-3}\)$$ sodium hydroxide. Step 3 Add the sodium hydroxide to the hydrochloric acid in the polystyrene cup. Stir the mixture and record the maximum temperature reached. Give a reason why an excess of sodium hydroxide was used. (1)

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