The enthalpy change for the reaction of hydrogen gas with fluorine gas to produce hydrogen fluoride is -542 kJ for the equation as written:
H2(g) + F2(g) ? 2 HF(g) ?H = -542 kJ

(a) What is the enthalpy change per mole of hydrogen fluoride produced?

(b) Is the reaction exothermic or endothermic as written?
exothermic endothermic

(c) What would be the enthalpy change for the reverse of the given equation (that is, for the decomposition of HF into its constituent elements)?