Question

in examples where the volume of a system is under constant pressure, which of the following quantities equals enthalpy change?
answer:
a work done by the system
b temperature change
c internal energy change
d heat absorbed or released by the system

Explanation:

Enthalpy change ($\Delta H$) at constant pressure is given by the formula $\Delta H=\Delta U + P\Delta V$, where $\Delta U$ is the change in internal energy, $P$ is pressure and $\Delta V$ is the change in volume. From the first law of thermodynamics, $\Delta U = q+w$ (where $q$ is heat and $w=-P\Delta V$ at constant pressure). Substituting $w$ in the enthalpy formula, we get $\Delta H = q$ (at constant pressure).

Answer:

D. heat absorbed or released by the system