1 The enthalpy of vaporization for a liquid corresponds to t

1. The enthalpy of vaporization for a liquid corresponds to the energy required to vaporize that liquid. The energy required during vaporization corresponds to breaking what kinds of attraction or bonds?

A) Would a compound with high vapor pressure at room temperature would have a high or low enthalpy of vaporization? Why?

B) Predict which liquid would have a higher enthalpy of vaporization: methanol or ethanol? Why?

Solution

The energy required during vaporization corresponds to breaking intermolecular focres of attraction between the molecules of the substances being vaporized, for example between ethanol molecules in case of vaporizing ethanol.Such forces include van der waal\'s forces of attraction, hydrogen bonding, etc.

A)At any temperature, boiling point occurs when vapor pressure of the substance equals the surrounding atmospheric pressure.So a compound having higher vapor pressure at room temperature means it would require less temperature increase before its vapor pressure equals the atmospheric pressure and thus would require less heat to vaporize the substance.In other words its enthalpy of vaporization would be lower.

B)Among short carbon chain alcohols as number of carbon atoms increase the boling point also increases because of increased van der waals forces-london dispersion forces of attraction.Hence ethanol has higher boiling point than methanol.