Chemistry 9701 · AS & A Level · Atoms, molecules and stoichiometry

Atoms, molecules and stoichiometry — practice question

Chemical reactions go hand in hand with enthalpy changes.
(a)[2]

Explain the meaning of standard enthalpy change of reaction.

(b(i))[1]

Calculate the amount of heat energy transferred to the water during this dissolving process. You may assume that the solution has the same specific heat capacity as water, $4.18\,\text{J g}^{-1}\text{K}^{-1}$.

(b(ii))[1]

Calculate the amount, in moles, of $\text{MgSO}_4$ dissolved.

(b(iii))[1]

Calculate the enthalpy change of solution, $\Delta H_{\text{soln}}$, of $\text{MgSO}_4(s)$. Include a sign in your answer.

(b(iv))[1]

Use the equation below for the hydration of anhydrous magnesium sulfate to construct an appropriate, fully labelled energy cycle that can be used to calculate the enthalpy change for this reaction, $\Delta H_{\text{hyd}}\,\text{MgSO}_4$. $\text{MgSO}_4(s) + 7\text{H}_2\text{O}(l) \rightarrow \text{MgSO}_4\cdot7\text{H}_2\text{O}(s)$

(b(v))[1]

Calculate the enthalpy change for this reaction, $\Delta H_{\text{hyd}}\,\text{MgSO}_4$. Your answer must include a sign.

Worked solution & mark scheme

This 7-mark question has a full step-by-step worked solution and mark scheme. One marking point: Heat or energy change at constant pressure OR $H_{\text{prod}} - H_{\text{react}}$

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