Problem: The heat of vaporization of water at 373 K is 40.7 kJ/mol.Find q for the evaporation of 451 g of water at this temperature.

We’re being asked to determine the heat (q) of the evaporation of 451 g of water at 373 K.

Recall that heat will be absorbed when water is being evaporated (phase change). Calculate heat (q) using the equation:

$\boxed{\mathbf{q}\mathbf{=}\mathbf{n}\mathbf{·}\mathbf{∆}{\mathbf{H}}_{\mathbf{vap}}}$

q = heat, J
n = number of moles (mol)
ΔH_vap = heat of vaporization, kJ/mol