Chemistry 9701 · AS & A Level · Chemical energetics

Chemical energetics — practice question

The standard enthalpy changes of formation for HCl and HI are $-92\ \text{kJ mol}^{-1}$ and $+26\ \text{kJ mol}^{-1}$ respectively. Which statement is the most significant for accounting for this difference?

  • AChlorine is more electronegative than iodine.
  • BThe activation energy for the $\text{H}_2 + \text{Cl}_2$ reaction is much less than that for the $\text{H}_2 + \text{I}_2$ reaction.
  • CThe bond energy of HI is smaller than the bond energy of HCl.
  • DThe bond energy of $\text{I}_2$ is smaller than the bond energy of $\text{Cl}_2$.

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