Chemistry 9701 · AS & A Level · Chemical energetics

Chemical energetics — practice question

At $550^\circ\text{C}$, nitrogen dioxide reacts with unburnt hydrocarbon fragments such as $\text{CH}_3$ inside the catalytic converter of a motor vehicle. $4\text{CH}_3 + 7\text{NO}_2 \rightarrow 3\frac{1}{2}\text{N}_2 + 4\text{CO}_2 + 6\text{H}_2\text{O}$ Which row shows the energy change for this reaction and a reason that could explain it?

  • Aendothermic; chemical energy is converted to heat energy
  • Bendothermic; the $\text{N}\equiv\text{N}$ bond energy is very high
  • Cexothermic; $\text{CO}_2$ and $\text{H}_2\text{O}$ have negative $\Delta H_f^\circ$ values
  • Dexothermic; double bonds are broken in $\text{NO}_2$

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