In the Clausius-Clapeyron equation, what is assumed about the condensed phase?

The Clausius-Clapeyron equation describes the relationship between the vapor pressure of a substance and its temperature, often applied to phase transitions such as sublimation and vaporization. One of the key assumptions in the derivation of this equation is related to the molar volumes of the condensed and vapor phases.

The correct choice indicates that the molar volume of the condensed phase is negligible compared to that of the vapor phase. This assumption is crucial because, in a gas, molecules are far apart and occupy a much larger volume than in a condensed phase (liuid or solid), where molecules are closely packed together. By assuming the condensed phase's molar volume is negligible, it simplifies the equation and allows for a more straightforward calculation of the changes in pressure and temperature during phase transitions.

This assumption holds true particularly for gases, as their molar volumes are significantly larger due to the distances between gas particles, and enables the use of the ideal gas approximation in calculations related to vapor pressures. Overall, this assumption is fundamental for the practical application of the Clausius-Clapeyron equation in thermodynamics when analyzing phase equilibria.