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, Pvap. 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(P2) = Ln(P1) + (delta H vap/R) * (1/T1 - 1/T2) where P2 and P1 are the vapor pressures that correspond to temperatures T2 and T1, respectively, delta H vap is the molar heat of vaporization, and R= 8.3145 J/mol*K is the gas constant. The vapor pressure of dichloromethane, CH2Cl2, at 0 degrees Celsius is 134 mmHg . The normal boiling point of dichloromethane is 40 degrees Celsius. Calculate its molar heat of vaporization.

Explanation / Answer

P1=134mmHg
T1=273K
T2=313K
P2=760mmHg, figured it out by cross multiplying.
R=8.3145J/ Mol K

Rearrange the Clapeyron equation so that molar heat is by itself and your answer is 3.09 X 10^4J/mol or 30.9KJ/mol

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