In the context of enthalpy, what does the equation ∆H = ∆U + P∆V represent?

The equation ∆H = ∆U + P∆V represents the relationship between the change in enthalpy (∆H), the change in internal energy (∆U), and the pressure-volume work done by or on a system, represented by the term P∆V. This equation is derived from the definition of enthalpy, which is defined as H = U + PV.

Under conditions of constant pressure, which is common in many chemical reactions, the change in enthalpy is particularly useful for understanding heat transfer during processes like reactions in an open system. When the pressure remains constant, any work done resulting from volume change (P∆V) simply adds to the change in internal energy to give the total change in enthalpy. Therefore, the correct interpretation of this equation in thermodynamics—especially in the context of chemical reactions and processes occurring at constant pressure—leads to the conclusion that ∆H represents the change in enthalpy, highlighting the energy changes involved in such reactions.

The other choices do not accurately represent the relationship expressed in the equation. For example, the equation does not simplify to a constant volume context nor does it pertain to calculating entropy changes. It specifically pertains to conditions at constant pressure, making