The thermal effect of chemical reaction refers to the heat released by the reaction. In the case that there is no volume work at constant pressure or volume work at constant volume, heat is equal to δU or δh, and thermodynamic energy and enthalpy are state functions, and their change values are only related to the state of the starting and ending state, and have nothing to do with the process.

Here, the causal relationship is reversed. Because the heat is equal to Δ u or Δ h under the condition of constant pressure without volume work or constant volume without volume work, its change value is only related to the state of the starting and ending state, and has nothing to do with the process. In fact, the thermal effect of chemical reaction is related to the way.