Concept explainers
PRACTICE 11.1 The boiling point of ethanol is 78.4 °C, and the enthalpy change for theconversion of liquid to vapor is
Interpretation:The boiling point of ethanol is 78.4
Concept introductionWhen a liquid undergoes vaporization, its entropy increases. Thus, the change in entropy is always positive for vaporization. This is due to the change of phase from liquid to vapor
The relation between change in Gibbs free energy, change in enthalpy and change in entropy is as follows:
In the vaporization of liquid, the liquid and vapor phases exist in equilibrium thus, the change in Gibbs free energy is zero.
Thus,
Or,
Given:The enthalpy change for vaporization,
Answer to Problem 11.1P
Solution:The value of
Explanation of Solution
Converting the boiling point from degree Celsius to Kelvin as follows:
The enthalpy change for the vaporization is 38.56 kJ/mol. Thus, the entropy change for the vaporization can be calculated as follows:
Putting the values,
Therefore, the value of
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