All liquids evaporate to a certain extent. The pressure exerted by the gas phase

Question

All liquids evaporate to a certain extent. The pressure exerted by the gas phase in equilibrium with the liquid is called vapor pressure, P_vap. The vapor pressure of a particular substance is determined by the strength of the intermolecular forces. But for any given substance the vapor pressure only changes with temperature. The Clausius-Clapeyron equation expresses the relationship between vapor pressure and temperature: ln P_2 = ln P_1 + (delta H_vap/R) (1/T_1 - 1/T_2) where P_1 and P_2 are the vapor pressures that correspond to temperatures T_1 and T_2 respectively. delta H_vap is the molar heat of vaporization, and R = 8.3145 J/(mol middot K) is the gas constant. Consider the following two substances and their vapor pressures at 298 K. Based on information, compare the characteristics of the two substances. Drag each item to the appropriate bin.

Explanation / Answer

Higher vapour pressure indicates weaker intermolecular forces, low boiling point, low heat of vaporisation.

So,

Substnace A: Has higher heat of vaporisation because its vapour pressure is low

                    Has a high boiling point.

Substance B: Has weaker intermolecular forces because its vapour pressure is high

                   is gas at 300 mmHg because it vapour pressure is 475 mmHg

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