This question is about enthalpy changes. A student wanted to use Hess's Law to determine the enthalpy change, $$\(\Delta_{\mathrm{r}} H_{1}\)$$, in $$\(\mathrm{kJ} \mathrm{mol}^{-1}\)$$, for Reaction 1. The student carried out an experiment to determine the enthalpy change of reaction, $$\(\Delta_{\mathrm{r}} \mathrm{H}_{2}\)$$, in $$\(\mathrm{kJ} \mathrm{mol}^{-1}\)$$, for Reaction 2. Reaction $$\(2 \mathrm{MgO}(\mathrm{s})+2 \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{MgCl}_{2}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \quad \Delta_{\mathrm{r}} \mathrm{H}_{2}\)$$ 0.189 g of solid magnesium oxide was added to excess hydrochloric acid in a During the experiment, the temperature increased from $$\(21.5^{\circ} \mathrm{C}\)$$ to $$\(28.0^{\circ} \mathrm{C}\)$$. VIHV SUH LMIAYM ION OO polystyrene cup and stirred until the reaction was complete. The total mass of the solution formed was 25.0 g . Calculate $$\(\Delta_{\mathrm{r}} \mathrm{H}_{2}\)$$, in $$\(\mathrm{kJ} \mathrm{mol}^{-1}\)$$, including a sign. Give your answer to an appropriate number of significant figures. [Specific heat capacity of the solution $$\(=4.18 \mathrm{~J} \mathrm{~g}^{-10} \mathrm{C}^{-1}\)$$. ] (4) VIZV SIHI NI BH\&M ION OO

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