![]() The process of evaporation is represented by a horizontal line on temperature entropy diagram. The thermodynamics of phase transitions of nine polyhydric alcohols have been studied by different experimental approaches. The boiling point is defined as that temperature where the vapor pressure of the material matches the ambient pressure. During the change of state, the temperature remains constant. Recall that substances can be made to boil at a large range of temperatures depending on that substance's phase diagram as long as we increase or reduce the ambient pressure. If we want to know the entropy associated with the vaporization of a material at a temperature other than that at standard pressure, we can use the procedure of calculating the entropy associated with bringing the material from its non standard boiling point to its standard (normal) boiling point, calculating the entropy associated with this vaporization phase change at that standard (normal) boiling point using the enthalpy of vaporization as q rev, then calculating the entropy change associated with cooling that material back down to the non standard (non normal) boiling temperature we are interested in. The (latent) heat of vaporization (Hvap) also known as the enthalpy of vaporization or evaporation, is the amount of energy (enthalpy) that must be added. ![]() We need molar heat capacities because they are used to determine q which in turn comprises the numerator of our definition of macroscopic entropy change dS = q rev/T. Which one of the following has the maximum entropy of vaporization 1.
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