Physics 2007 JAMB Past Questions - Question 35: I increase the melting point of the liquid II increase the boiling point of the liquid III. Decrease the melting point of the liquid. . iv decrease the boiling point of the liquid. Which of the statements above about the effects of increase in pressure in a liquid are correct?

Correct Answer

B

Explanation

Increase in pressure generally raises the boiling point but lowers the melting point. II and III

When you increase the pressure on a liquid, it can affect the melting point and boiling point differently depending on the substance. Let's break down the statements:

I. Increase the melting point of the liquid:
  - True for most substances: An increase in pressure tends to increase the melting point of a substance. This is because the higher pressure makes it more difficult for the molecules to move into the less dense, ordered solid phase.

II. Increase the boiling point of the liquid:
  - True for most substances: An increase in pressure also tends to increase the boiling point of a substance. This is because higher pressure makes it more difficult for the molecules to escape into the vapor phase, requiring higher temperatures to achieve the necessary vapor pressure.

III. Decrease the melting point of the liquid:
  - Generally false: Increasing pressure typically raises the melting point, not decreases it. This is the opposite of what happens.

IV. Decrease the boiling point of the liquid:
  - Generally false: Increasing pressure typically raises the boiling point, not decreases it.

So, the correct statements are I and II. An increase in pressure tends to increase both the melting and boiling points of a liquid.