Question

A quantity of water was vaporized completely in a piston-cylinder apparatus at 100oc against a constant pressure of 1.00 atm. during the process, 22.6 kj of heat flowed into the system which did 1.70 kj of work on the surroundings. what is the enthalpy change of the system?

Answer 1

Enthalpy change of a system is equal to the difference of internal energy and the work involved in the system. Internal energy is equal to the sum of heat and work in a system. We can relate these things to calculate for the enthalpy as follows:

H = U - W

since U = Q + W

H = Q + W - W
H = Q
H = 22.6 kJ

Hope this helps.