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JAMB Chemistry 1998 Question 26

Question 26

Energy Changes

The reaction that is accompanied by a decrease in entropy when carried out at constant temperature is

  1. A.N2O4(g) ⇌ 2NO2(g)
  2. B.N2(g) + 3H2(g) ⇌ 2NH3(g)
  3. C.CaCO3(s) ⇌ CaO(s) + CO2(g)
  4. D.2N2H4(l) + N2O4(l) ⇌ 3N2(g) + 4H2O(l)
Show the answer and explanation

Answer: B (N2(g) + 3H2(g) ⇌ 2NH3(g))

Explanation

Entropy (disorder) falls when the number of gas molecules falls. In B, 4 moles of gas become 2 moles; the other reactions produce more gas.