IB Chemistry SL 1.1.4 Standard Enthalpy Change H Questions

Use real exam questions to calculate heat transfer, convert calorimetry data into molar enthalpy and evaluate temperature evidence and heat loss.

Exam points

Calculate heat transferred at constant pressure with q = mcΔT, using mass, specific heat capacity, temperature change and consistent units.
Convert measured heat into molar enthalpy change using amount of substance or stoichiometry, with the correct sign and kJ mol⁻¹ units.
Use calorimetry observations, temperature changes and experimental assumptions or heat-loss evidence to compare the energy change of reactions or dissolutions.

[Maximum number: 2]

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.

Table for Question IB Chemistry SL 1.1.4 Standard Enthalpy Change H Questions question 1 — IB Chemistry SL

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.

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IB Chemistry SL 1.1.4 Standard Enthalpy Change H Questions question 1