Part A Chemical energy is released or absorbed from reactions in various forms The most easily measurable form of energy comes in the form of heat or enthalpy. The enthalpy of a reaction can be calculated from the heats of formation of the substances involved in the reaction AH = 11,4H" (products) - En, A H" (reactants) where i represents the stoichiometric coefficients Calculate the standard enthalpy change for the reaction 2A+B=20 +2D Use the following data Substance " (kJ mol 247 B 395 C 203 D -503 Express your answer to three significant figures and include the appropriate units. View Available Hind HA th 02 AH Value KJ. mol