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JAMB Chemistry 1989 Question 3

Question 3

Kinetic Theory and States of Matter

From the vapour pressure curves of liquids I, II and III shown, it can be deduced that

Diagram for this question
  1. A.liquid I has the highest boiling point
  2. B.liquid II has the highest boiling point
  3. C.liquid III has the highest boiling point
  4. D.liquid III has the lowest boiling point.
Show the answer and explanation

Answer: C (liquid III has the highest boiling point)

Explanation

A liquid boils when its vapour pressure reaches the external pressure (the horizontal line). Liquid III reaches it at the highest temperature, so it has the highest boiling point.