Regarding change in enthalpy and its causes

Question

delta H = delta U + P*delta V. Textbook says that this means a change in enthalpy could either be due to a change in internal energy OR expansion/compression work. But in a constant pressure condition, how can you change internal energy without changing volume and vice versa ? So can they be independently changed or not ?

Young Kindaichi · Accepted Answer

The Enthalpy is given by
$$H=U+pVRightarrow dH=dU+d(pV)=TdS+Vdp$$
So the enthalpy can be changed by either change of $S$ and $p$.
The expression is given by OP

$$dH=dU+pdV    text{not true in general}$$

If the  process is isobaric (constant pressure )
$$dH=TdS   text{(Isobaric process)}$$
The right side is just Heat (assuming reversible process). So at the constant process, the enthalpy can be changed by Heat.

Regarding change in enthalpy and its causes

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