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JAMB Chemistry 2006 Question 49

Question 49

Energy Changes

If the heat of combustion of hydrogen is −285.8kJ, what is the heat of formation of water?

  1. A.+571.6 kJ
  2. B.−571.6 kJ
  3. C.−285.8 kJ
  4. D.+285.8 kJ
Show the answer and explanation

Answer: C (−285.8 kJ)

Explanation

Burning one mole of hydrogen (H2 + ½O2 → H2O) is the same reaction as forming one mole of water from its elements, so both are −285.8 kJ.