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Magnesium sulfate can exist in either the hydrated form or in the anhydrous form. Two students wished to determine the enthalpy of hydration of anhydrous magnesium sulfate. They measured the initial and the highest temperature reached when anhydrous magnesium sulfate, $\mathrm{MgSO}_{4}(\mathrm{~s})$ , was dissolved in water. They presented their results in the following table.

Calculate the enthalpy change, $\Delta H_{1}$ , for anhydrous magnesium sulfate dissolving in water, in $\mathrm{kJ} \mathrm{mol}^{-1}$ . State your answer to the correct number of significant figures.

energy released $=50.0 \times 4.18 \times 9.7=2027(\mathrm{~J}) / 2.027(\mathrm{~kJ})$ ;
$\Delta H_{1}=-81\left(\mathrm{~kJ} \mathrm{~mol}^{-1}\right) ;$

Marking guidance:

Award [2] for correct answer.
Award [2] if 53.01 is used giving an answer of $-86\left(\mathrm{~kJ} \mathrm{~mol}^{-1}\right)$ .
Award [1 max] for $+81 / 81 /+86 / 86\left(\mathrm{~kJ} \mathrm{~mol}^{-1}\right)$ .
Award [1 max] for -81000/-86000 if units are stated as $\mathrm{J} \mathrm{mol}^{-1}$ .
Allow answers to 3 significant figures.

IB Chemistry SL 1.1.4 Standard Enthalpy Change H Topic Practice

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IB Chemistry SL 1.1.4 Standard Enthalpy Change H Topic Practice

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Question 1