Recall, by definition a
change in energy equals heat transferred (q) plus work
(w):
DE = q + w
Consider a process carried
out at constant pressure. At constant
pressure, work involves only a change in volume. We can
then substitute -PDV
for w.
DE = qp - PDV
Then if we want to solve
for the heat transferred, qp, at constant
pressure, we simply rearrange the equation.
qp = DE + PDV
At Constant
Pressure