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JAMB Chemistry 2005 Question 6

Question 6

Energy Changes

2H2 + O2 → 2H2O ΔH = −571 kJ
In the equation above, how much heat will be liberated if 12.0g of hydrogen is burnt in excess oxygen?

  1. A.−1142 kJ
  2. B.−571 kJ
  3. C.+1142 kJ
  4. D.−1713 kJ
Show the answer and explanation

Answer: D (−1713 kJ)

Explanation

2 mol H2 = 4.0 g releases 571 kJ. 12.0 g is three times that, so ΔH = 3 × (−571) = −1713 kJ.