Calculate the standard enthalpy change for the reaction2A+B⇌2C+2D Use the following data: Substance ΔH∘f (kJ/mol) A -227 B -413 C 175 D -521 Express your answer to three significant figures and include the appropriate units (note: the problem asks for the standard enthalpy of the reaction as written, so the units are not 'per mol'). View Available Hint(s)