Question

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:

ΔH∘rxn=Σ npΔH∘f(products)−Σ nrΔH∘f(reactants)

where n represents the stoichiometric coefficients.

Calculate the standard enthalpy change for the reaction

2A+B⇌2C+2D

Use the following data:

Substance	ΔH∘f (kJ/mol)
A	-231
B	-407
C	219
D	-497