The enthalpy of vaporization for water is 40.67 kJ/mol and the enthalpy of fusion for water is
6.01 kJ/mol. What is the enthalpy of deposition?
The Correct Answer and Explanation is:
The enthalpy of deposition is the amount of energy released when a substance transitions directly from a gas to a solid without passing through the liquid phase. In the case of water, this process involves water vapor transitioning directly to ice. To find the enthalpy of deposition, we can use the enthalpy values for fusion and vaporization.
Calculation of Enthalpy of Deposition
The relationship between the enthalpy of deposition ((ΔH_{deposition})), the enthalpy of vaporization ((ΔH_{vap})), and the enthalpy of fusion ((ΔH_{fus})) for a substance is given by the equation:
[
ΔH_{deposition} = -ΔH_{vap} + (-ΔH_{fus})
]
Where:
- (ΔH_{vap} = 40.67 \, \text{kJ/mol}) (enthalpy of vaporization)
- (ΔH_{fus} = 6.01 \, \text{kJ/mol}) (enthalpy of fusion)
Substituting the values into the equation:
[
ΔH_{deposition} = -40.67 \, \text{kJ/mol} – 6.01 \, \text{kJ/mol}
]
[
ΔH_{deposition} = -46.68 \, \text{kJ/mol}
]
Thus, the enthalpy of deposition for water is −46.68 kJ/mol.
Explanation
Enthalpy changes are crucial in understanding phase transitions in thermodynamics. The enthalpy of vaporization indicates the energy required to convert water from a liquid to a gas, whereas the enthalpy of fusion refers to the energy needed to convert ice (solid) to water (liquid).
When water vapor deposits directly into ice, energy is released instead of being absorbed. The negative sign in the enthalpy of deposition indicates an exothermic process, which means that the system (water vapor) releases energy to the surroundings as it transitions to the solid phase. This process is relevant in various natural phenomena, such as frost formation on surfaces and snowflake development in the atmosphere.
Understanding these enthalpy changes is essential for fields like meteorology, environmental science, and engineering, where controlling temperature and phase transitions is often crucial for efficiency and effectiveness in systems involving water.