A three-step reaction proceeds through two intermediates. The enthalpy of the reactants is set at 0 kJ. After the first step, the enthalpy is +10 kJ; after the second step, it is –30 kJ; the products have an enthalpy of –50 kJ. What is the overall ΔH for the reaction?
a) −40 kJ
b) +50 kJ
c) −50 kJ
d) −30 kJ