Exothermic reaction has negative enthalpy change because energy is flowing out of the system. Isolated system means no energy is flowing in and out of the system. If you have an exothermic reaction in an isolated system, is enthalpy change 0?
Substance 1: initial enthalpy of isolated system (i.e. reactants) is H1.
Substance 2: Enthalpy of isolated system after reaction (i.e products) is H2.
Substance 3: Enthalpy of products taken out of isolated system, and left to be cooled (i.e. products cooled down to room temperature) is H3
Is enthalpy change of reaction H2-H1? H3-H1? Or neither?
Correct me if I am wrong: If you have a sealed container with gas at 500K, the gas loses heat energy to its surroundings, then there is an enthalpy change. Since substance 3 is at a lower temp than substance 2, H3 is not equal to H2.