The molar enthalpy of vaporisation ($\Delta H_{vap}$) of a liquid is the enthalpy change when one mole of liquid is converted to vapour at its boiling point.

A chemist performs an experiment to determine $\Delta H_{vap}$ for tetrachloromethane (${CCl}_4$).

The chemist:

• places a flask containing tetrachloromethane on a continuous-recording balance
• uses an immersed electrical heating element rated at $0.85kW$ to bring the liquid to its boiling point ($76.7{}^{\circ }C$)
• records the initial mass once steady boiling is established
• maintains the heating at $0.85kW$ for exactly $5.0minutes$ ($300s$)
• records the final mass of the flask and remaining liquid.

The mass of tetrachloromethane vaporised and lost from the flask during this period is $1.31kg$.

Calculate the molar enthalpy of vaporisation, $\Delta H_{vap}$, for tetrachloromethane in ${kJ\; mol}^{-1}$.

(Molar mass of ${CCl}_4=154.0{g\; mol}^{-1}$)

$[1kW=1{kJ\; s}^{-1}]$