Enthalpy, H

Applying the first law to a closed system requires two more state functions: enthalpy ($H$), and the heat capacity that relates a temperature change to the heat absorbed. This part develops both, along with the extensive/intensive distinction that decides which quantities scale with the amount of substance:

• A Useful New State Function — why enthalpy is defined, and how $\Delta H$ relates to $\Delta U$.
• Extensive and Intensive Properties — which properties double when the system doubles, and which don't. …