Question

the change in this thermodynamic function equals heat flow when pressure is constant.

options: calorie, joule, endothermic, exothermic, adiabatic, enthalpy, internal energy, work, or phase change

Answer 1

Answer: Enthalpy.

At constant pressure, the heat flow for any process is equal to the change in the internal energy of the system plus the PV work done. Because conditions of constant pressure are so important in chemistry, a new state function called enthalpy (H) is defined as:

H=U+PV

At constant pressure, the change in the enthalpy of a system is as follows:
∆H = ∆U + P∆V

Comparing the previous two equations shows that at constant pressure, the change in the enthalpy of a system is equal to the heat flow: ΔH=qp. Therefore, definition of enthalpy is that enthalpy is the heat absorbed or produced during any process that occurs at constant pressure.

At constant pressure, the change in the enthalpy of a system is equal to the heat flow: ΔH=qp.

Hence, the correct answer is Enthalpy.