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: rH= npfH(products) nrfH(reactants) where n represents the stoichiometric coefficients. Part A Calculate the standard enthalpy change for the reaction 2A+B2C+2D Use the following data: Substance fH ( kJ mol1) A -241 B -385 C 175 D -475 Express your answer to three significant figures and include the appropriate units.