When a reaction involves only solids, liquids, or liquid solutions, the change in enthalpy is equal to the change in internal energy.

Question

Quizplus · Accepted Answer

This is because the work done by or on the system due to volume changes is negligible in comparison to the heat flow in such reactions. Therefore, the only significant energy change is the heat exchanged between the system and the surroundings, which is equal to the change in enthalpy (assuming constant pressure).

When a Reaction Involves Only Solids, Liquids, or Liquid Solutions