The definition of enthalpy as a function of heat capacity and temperature change. $ \Delta H = C_p \Delta T $.
Does it only apply at constant pressure? In my discussions on this board and also with links elsewhere, it looks like this equation applies during the Carnot Cycle, where there is no constant pressure.
I generally think this equation does not need constant pressure to apply. However today, when I was going through Atkins Physical Chemistry, it specifically says:
$ \Delta H = C_p \Delta T $ (at constant pressure)
equation 2B.6b. I think the constant pressure part is wrong, but this is a book with 10 editions with 5 star reviews on amazon.