Question

The following paragraphs should be calculated assuming that the molar volume of Ethanol in its gaseous phase is far larger than its molar volume in either the solid or liquid phases.

Moreover, one should assume that the enthalpy involved in the transition between phases does not change with temperature.

Ethanol boils at 73.30 degrees Celsius at atmospheric pressure. The heat of vaporization, ΔΗ_vapis 39.3 kJ/mol. The melting point at atmospheric pressure is -114.10 degrees Celsius. The triple point is at pressure 0.00043 Pa and temperature -123.00 degrees Celsius. The density of liquid Ethanol at 25.0 degrees Celsius is 0.783 gr/cm³.

1. What is the vapor pressure of liquid ethanol at 30.00 degrees Celsius?
2. The heat of fusionΔΗ_meltis 4.9 kJ/mol. Calculate the change in volume brought about by a transition from the liquid phase to the solid phase at 300 K. Assume that the coexistence curve solid-liquid is a straight line with a constant slope along its entire trajectory. Is the result logical?
3. Draw the phase diagram, including the points referred to in the question.

Answer 1

For calculating the vapour pressure of liquid ethanol at 30.00 degrees Celsius,

For calculating the change in volume brought about by a transition from the liquid phase and solid phase at 300 K,

Yes, the result coming out is logical. According to Clausius Clapeyron equation, as the volume change for the fusion curve is positive and the molar enthalpy is positive. This shows the slope for the curve is positive.