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JAMB Chemistry 1993 Question 8

Question 8

Kinetic Theory and States of Matter

For iodine crystals to sublime on heating, the molecules must acquire energy that is

  1. A.less than the forces of attraction in the solid
  2. B.equal to the forces of attraction in the solid
  3. C.necessary to melt the solid
  4. D.greater than the forces of attraction in both the solid and the liquid phases
Show the answer and explanation

Answer: D (greater than the forces of attraction in both the solid and the liquid phases)

Explanation

In sublimation the solid goes straight to vapour, skipping the liquid. The molecules need enough energy to break free of all the attractions that would hold them as a solid or a liquid.