N2(g) + 3H2(g) --> 2NH3(g); ΔH = -91.8 kJ Consider the thermochemical equation for the synthesis of ammonia. Which statement is true?

a. negative enthalpy indicates that energy is required to complete the reaction.

b. Negative enthalpy indicates a decrease in potential energy and an endothermic reaction.

c. Enthalpy is negative indicating that energy is released so this is an exothermic reaction.

d. Enthalpy is negative indicating that there is an energy deficit; the reaction is incomplete.