Chemistry 9701 · AS & A Level · Chemical energetics

Chemical energetics — practice question

The enthalpy change values for the reactions that may occur are shown below. W: $\text{NaOH(aq)} + \text{HCl(aq)} \rightarrow \text{NaCl(aq)} + \text{H}_2\text{O(l)}\quad \Delta H^\circ = -56\,\text{kJ mol}^{-1}$ X: $\text{NaCl(aq)} + \text{H}_2\text{O(l)} \rightarrow \text{NaOH(aq)} + \text{HCl(aq)}\quad \Delta H^\circ = +56\,\text{kJ mol}^{-1}$ Y: $2\text{HI(g)} \rightarrow \text{H}_2\text{(g)} + \text{I}_2\text{(g)}\quad \Delta H^\circ = +11\,\text{kJ mol}^{-1}$ Z: $\text{H}_2\text{(g)} + \text{I}_2\text{(g)} \rightarrow 2\text{HI(g)}\quad \Delta H^\circ = -11\,\text{kJ mol}^{-1}$ Which statement concerning the activation energies of these reactions is correct?

  • AX is greater than W; Z is greater than Y.
  • BX is greater than W; Y is greater than Z.
  • CW is greater than X; Z is greater than Y.
  • DW is greater than X; Y is greater than Z.

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