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JAMB Chemistry 1978 Question 4

Question 4

Energy Changes

When sodium chloride and metallic sodium are each dissolved in water

  1. A.both processes are exothermic
  2. B.both processes are endothermic
  3. C.the dissolution of metallic sodium is endothermic
  4. D.the dissolution of metallic sodium is exothermic
  5. E.the dissolution of sodium chloride is explosive.
Show the answer and explanation

Answer: D (the dissolution of metallic sodium is exothermic)

Explanation

Sodium reacts vigorously with water, giving out a lot of heat, so it is exothermic. Dissolving sodium chloride absorbs a little heat (slightly endothermic).