Understanding the Concepts
* Entropy of Vaporization (ΔSvap): This is the change in entropy when a substance transitions from a liquid to a gas. It represents the increase in disorder or randomness of the molecules.
* Enthalpy of Vaporization (ΔHvap): This is the amount of energy required to vaporize one mole of a substance at its boiling point.
* Boiling Point: The temperature at which a liquid's vapor pressure equals the surrounding atmospheric pressure.
The Equation
The relationship between enthalpy change (ΔHvap), entropy change (ΔSvap), and boiling point (T) is given by the following equation:
ΔSvap = ΔHvap / T
Important Note: The temperature (T) must be in Kelvin!
Calculations
1. Convert the boiling point to Kelvin:
T = 78.5 °C + 273.15 = 351.65 K
2. Plug the values into the equation:
ΔSvap = 109.8 J/mol·K / 351.65 K
3. Calculate the entropy of vaporization:
ΔSvap ≈ 0.312 J/mol·K
Answer: The entropy of vaporization per mole of ethanol is approximately 0.312 J/mol·K.
