Enthalpy is defined as the sum of internal energy (U) and the product of pressure (P) and volume (V), expressed as H = U + PV. The discussion clarifies that while the equations for enthalpy change and heat transfer may appear similar, they apply to different scenarios. In processes like fluid flow through a pipe, the heat added or removed corresponds to the change in enthalpy. Conversely, in a sealed container where heat is added, the heat transfer relates to the change in internal energy. Enthalpy is recognized as a property of a substance, while heat is viewed as a transport phenomenon, emphasizing that heat itself is not a property. At constant pressure, the change in enthalpy equates to the heat transfer in specific situations.
