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3.2 Energetics

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Question 23
H

Methane reacts with chlorine to make chloromethane and hydrogen chloride.

CH4+Cl2→CH3Cl+HCl \mathrm{CH_{4} + Cl_{2} \rightarrow CH_{3}Cl + HCl} CH4​+Cl2​→CH3​Cl+HCl

A methane molecule has four C−H\mathrm{C{-}H}C−H bonds. A chloromethane molecule has three C−H\mathrm{C{-}H}C−H bonds and one C−Cl\mathrm{C{-}Cl}C−Cl bond.

BondC−H\mathrm{C{-}H}C−HCl−Cl\mathrm{Cl{-}Cl}Cl−ClC−Cl\mathrm{C{-}Cl}C−ClH−Cl\mathrm{H{-}Cl}H−Cl
Bond energy (kJ/mol\mathrm{kJ/mol}kJ/mol)413243346432

What is the energy change for the reaction?

[1]
A

+122 kJ/mol+122\,\mathrm{kJ/mol}+122kJ/mol

B

+310 kJ/mol+310\,\mathrm{kJ/mol}+310kJ/mol

C

−535 kJ/mol-535\,\mathrm{kJ/mol}−535kJ/mol

D

−122 kJ/mol-122\,\mathrm{kJ/mol}−122kJ/mol

Markscheme

3.2 Energetics Questions

  1. GCSE
  2. /Chemistry
  3. /3.2 Energetics

51 exam-style questions on OCR GCSE Chemistry 3.2 Energetics, covering 3.2.1 Exothermic and endothermic reactions and reaction profiles and 3.2.2 Calculating energy change from bond energies. Each one has a worked solution and a mark scheme showing where the marks go.

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