Heat of sublimation can be approximated by adding together
A) heat of freezing (solidification), heat of vaporization
B) heat of deposition, heat of vaporization
C) heat of freezing (solidification), heat of condensation
D) heat of fusion, heat of vaporization
E) heat of fusion, heat of condensation
The correct answer and explanation is :
The correct answer is:
D) Heat of fusion, heat of vaporization
Explanation:
Sublimation is the process in which a solid changes directly into a gas without passing through the liquid phase. The heat required for this phase change is called the heat of sublimation (ΔH_sub).
To approximate the heat of sublimation, we can consider the energy required to first convert the solid into a liquid (melting) and then the energy needed to convert the liquid into a gas (vaporization).
- Heat of fusion (ΔH_fus): This is the energy required to convert a solid into a liquid at its melting point. During this process, intermolecular forces are partially overcome, allowing the molecules to move more freely.
- Heat of vaporization (ΔH_vap): This is the energy required to convert a liquid into a gas at its boiling point. In this step, the remaining intermolecular forces are completely overcome, allowing the molecules to escape into the gas phase.
Thus, the total energy required to change a solid directly into a gas can be approximated by summing the heat of fusion and the heat of vaporization:
[
ΔH_{sub} \approx ΔH_{fus} + ΔH_{vap}
]
Why Other Options Are Incorrect:
- A & C: Heat of freezing (solidification) and heat of condensation release energy, whereas sublimation requires energy input.
- B: Heat of deposition is the opposite of sublimation, so it does not contribute to the energy required for sublimation.
- E: Heat of condensation releases energy, while sublimation requires energy input.
Thus, the best approximation for the heat of sublimation is the sum of the heat of fusion and the heat of vaporization.
