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JAMB Chemistry 2006 Question 43

Question 43

Energy Changes

H2(g) + Br2(g) → 2HBr(g)
The reaction above is carried out at 25°C. If ΔH is −72 kJ mol−1 and ΔS is − 106 J mol−1 K−1, the reaction will

  1. A.not proceed spontaneously at the given temperature
  2. B.proceed spontaneously at the given temperature
  3. C.proceed in the reverse direction at the given temperature
  4. D.proceed spontaneously at lower temperatures.
Show the answer and explanation

Answer: B (proceed spontaneously at the given temperature)

Explanation

ΔG = ΔH − TΔS = −72 − (298 × −0.106) = −72 + 31.6 = −40.4 kJ mol−1. A negative ΔG means it proceeds spontaneously at 25°C.