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JAMB Chemistry 1982 Question 4

Question 4

Kinetic Theory and States of Matter

When a pressure cooker is half filled with water, and heated to boiling point, then the pressure inside the cooker will

  1. A.decrease, since only a fraction of the water molecules has changed to vapour
  2. B.remain constant, because the total number of water molecules has not changed
  3. C.increase, because the water molecules can now reach every part of the sealed tube
  4. D.decrease, since water boils under reduced pressure
  5. E.increase, because the water vapour molecules now strike the walls of the tube more frequently because of their increased velocity
Show the answer and explanation

Answer: E (increase, because the water vapour molecules now strike the walls of the tube more frequently because of their increased velocity)

Explanation

Heating turns more water into vapour and makes the vapour molecules move faster, so they hit the walls more often and harder: the pressure rises.