The vapor pressure of liquid X is lower than that of liquid...

The vapor pressure of liquid $X$ is lower than that of liquid $Y$ at $20^{\circ} \mathrm{C},$ but higher at $60^{\circ} \mathrm{C} .$ What can you deduce about the relative magnitude of the molar heats of vaporization of $X$ and $Y$ ?

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Key Concepts

Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature. It reflects the tendency of molecules to escape from the liquid phase and enter the gas phase and is a key indicator of volatility.

Temperature Dependence of Vapor Pressure

The vapor pressure of a liquid increases with temperature because higher temperatures provide more energy for molecules to overcome intermolecular forces and escape into the vapor phase. This relationship is fundamental in understanding phase transitions and the behavior of substances under varying thermal conditions.

Clausius-Clapeyron Equation

The Clausius-Clapeyron equation quantitatively relates the change in vapor pressure with temperature to the molar heat of vaporization. By connecting these variables, it allows prediction of how vapor pressure varies with temperature and provides insight into the energetic changes during phase transitions.

Molar Heat of Vaporization

The molar heat of vaporization is the amount of energy required to vaporize one mole of a liquid at constant temperature and pressure. It is directly related to the strength of intermolecular forces within the liquid; higher values indicate stronger attractions and thus a greater sensitivity of vapor pressure to changes in temperature.

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