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JAMB Chemistry 1993 Question 27

Question 27

Energy Changes

The standard enthalpies of formation of CO2(g), H2O(g) and CO(g) in kJ mol−1 are −394, −242 and −110 respectively. What is the standard enthalpy change for the reaction CO(g) + H2O(g) → CO2(g) + H2(g)?

  1. A.−42 kJ mol−1
  2. B.+42 kJ mol−1
  3. C.−262 kJ mol−1
  4. D.+262 kJ mol−1
Show the answer and explanation

Answer: A (−42 kJ mol−1)

Explanation

ΔH = ΣΔHf(products) − ΣΔHf(reactants) = (−394 + 0) − (−110 − 242) = −394 + 352 = −42 kJ mol−1.