Chemistry
posted by Sarah .
What is the value of q when 8.21g of water vaporizes at 373 K? The enthalpy of condensation of water at 373 K is 40.7 kJ/mol.
I tried using the equation q= m x Cs x Delta T, but I never got the right answer which is 18.5 kJ apparently, so I need to find out what I did wrong.

You used the correct formula for calculating q WITHIN a phase; however, the formula to use at a phase change is
q = mass x heat vap for boiling/condensing.
q = mass x heat fusion for freezing/melting.