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JAMB Chemistry 1989 Question 27

Question 27

Energy Changes

The combustion of ethene, C2H4, is given by the equation C2H4 + 3O2 → 2CO2 + 2H2O; ΔH = −1428 kJ. If the molar heats of formation of water and carbon (IV) oxide are −286 kJ and −396 kJ respectively, calculate the molar heat of formation of ethene in kJ

  1. A.−2792
  2. B.+2792
  3. C.−64
  4. D.+64
Show the answer and explanation

Answer: D (+64)

Explanation

ΔH = ΣH(products) − ΣH(reactants): −1428 = 2(−396) + 2(−286) − H(C2H4) = −1364 − H(C2H4). So H(C2H4) = +64 kJ.