1. The problem statement, all variables and given/known data I'm trying to understand two things: 1. How internal energy is distinct from kinetic and potential energy 2. The difference between internal energy and enthalpy. 2. Relevant equations enthalpy ΔH = ΔU + PΔV internal energy ΔU = Q + W = Q - PΔV 3. The attempt at a solution I have searched old posts. I found this. And this. My book asked a question: if an exothermic reaction occurs in a closed system, does internal energy change? The answer is no. So it seems that internal energy includes potential energy. Both pages that I linked say that E = KE + PE + U. This suggests that internal energy and potential energy are completely distinct, yet the book question suggests that they are the same! Also, how is internal energy different from enthalpy? thank you very much!