A student is preparing a written report on phase changes and wishes to include an energy diagram for the vaporization of liquid ethanol at its normal boiling point (78.4 °C, 1 atm). The student is unsure how to represent the process graphically.
(1) Describe in detail the essential features that must appear on a correctly constructed energy diagram for the vaporization of ethanol at 1 atm. Your description should include the orientation and labeling of both axes, the relative positions of the reactant and product energy levels, and any annotation of the enthalpy change.
(2) Explain how the diagram you described in part (a) would differ if it instead represented the condensation of ethanol vapor at 78.4 °C and 1 atm. In your explanation, account for the sign of the enthalpy change and the direction of energy flow.