Chemistry 9701 · AS & A Level · Chemical energetics

Chemical energetics — practice question

The bond energy data shown are listed here. Bond energies: C-H: $410\ \text{kJ mol}^{-1}$ C-Cl: $340\ \text{kJ mol}^{-1}$ Cl-Cl: $244\ \text{kJ mol}^{-1}$ Br-Br: $193\ \text{kJ mol}^{-1}$ These bond energy values correspond to the four reactions below: P: $\text{Br}_2 \rightarrow 2\text{Br}$ Q: $2\text{Cl} \rightarrow \text{Cl}_2$ R: $\text{CH}_3 + \text{Cl} \rightarrow \text{CH}_3\text{Cl}$ S: $\text{CH}_4 \rightarrow \text{CH}_3 + \text{H}$ In which sequence do the enthalpy changes of these reactions run from the most negative to the most positive?

  • AP → Q → R → S
  • BQ → R → S → P
  • CR → Q → P → S
  • DS → P → Q → R

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