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