Question

In the heating curve shown below, heat is applied to a solid substance at a constant rate.

What accounts for the fact that segment CD is longer than segment AB?
a) Boiling occurs at a higher temperature than melting.
b) The heat of vaporization is greater than the heat of fusion.
c) Average kinetic energy increases at a greater rate during boiling than during melting.
d) Potential energy is being released during boiling.

Answer 1

Segment CD is longer than segment AB in the heating curve because the heat of vaporization is greater than the heat of fusion.

Step-by-step explanation:

The fact that segment CD is longer than segment AB in the heating curve is due to b) The heat of vaporization is greater than the heat of fusion. Now, let's analyze the options:

a) Melting and boiling occur at different temperatures. Boiling usually occurs at a higher temperature than melting, but this doesn't explain why CD is longer than AB.

b) The heat of vaporization is the amount of heat required to change a substance from a liquid to a gas (during boiling), and the heat of fusion is the amount of heat required to change a substance from a solid to a liquid (during melting). If the heat of vaporization is greater than the heat of fusion, it means more heat is required to boil the substance than to melt it. This supports the idea that CD is longer than AB.

c) The rate of increase of average kinetic energy doesn't directly explain why one phase change requires more heat than another.

d) Releasing potential energy usually happens during phase changes where the substance transitions to a state with lower potential energy, such as from gas to liquid or liquid to solid. It doesn't directly explain why CD is longer than AB.

Therefore, option b) "The heat of vaporization is greater than the heat of fusion" is the most likely explanation for why segment CD is longer than segment AB in the heating curve.

During boiling, a substance undergoes a phase change from a liquid to a gas, which requires a larger amount of heat compared to the phase change from a solid to a liquid during melting. The heat of vaporization is the amount of energy required to convert 1 gram of a substance from a liquid to a gas, while the heat of fusion is the amount of energy needed to convert 1 gram of a substance from a solid to a liquid.

Answer 2

Segment CD is longer than segment AB on a heating curve because the heat of vaporization required during boiling is greater than the heat of fusion required during melting. So, the correct option is b) The heat of vaporization is greater than the heat of fusion.

Step-by-step explanation:

Why is Segment CD Longer Than Segment AB on a Heating Curve?

The reason why segment CD is longer than segment AB on a heating curve when heat is applied to a solid substance at a constant rate can be attributed to several factors.

As heat is applied to a substance, its temperature increases until it reaches the melting or boiling point.

At these points, the temperature remains constant while the substance undergoes a phase change.

The heat of vaporization, which is required during the boiling phase, is usually much greater than the heat of fusion, which is required during the melting phase.

This is the key reason for the disparity in length between segment CD (boiling phase) and segment AB (melting phase).

Therefore, the correct answer to the student's question is b) The heat of vaporization is greater than the heat of fusion.