The graphs in Figure P 10.5 have the same scales and...

The graphs in Figure $\mathrm{P} 10.5$ have the same scales and describe the change in $\ln \left(P_{\text {vap }}\right)$ of two pure liquids as a function of temperature. Which liquid has the stronger intermolecular attractive forces? Explain your answer.

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Key Concepts

Intermolecular Forces

Intermolecular forces include the forces of attraction between molecules, such as hydrogen bonds, dipole-dipole interactions, and van der Waals forces. In liquids, stronger intermolecular forces hold the molecules together more tightly, making it more difficult for them to escape into the vapor phase. This directly influences physical properties like boiling point and vapor pressure.

Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid (or solid) phase. A liquid with strong intermolecular attractions has a lower vapor pressure at a given temperature because fewer molecules have enough energy to overcome these attractions and enter the gas phase. Thus, comparing vapor pressure is a good indicator of the strength of the attractive forces in a liquid.

Clausius-Clapeyron Equation

The Clausius-Clapeyron equation provides a quantitative relation between vapor pressure and temperature, revealing that the slope of a plot of ln(vapor pressure) versus temperature (or 1/T) is related to the enthalpy of vaporization. A steeper slope indicates a higher enthalpy of vaporization, meaning more energy is required to overcome intermolecular attractions. Therefore, comparing such slopes or relative vapor pressures can indicate which liquid exhibits stronger intermolecular forces.

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