The enthalpy of formation for cap c sub 6 cap h sub 6 l is 49 point 0 kJ over mol Consider the reaction. 6 cap c open paren s comma graphite close paren plus 3 cap h sub 2 g rightarrow cap c sub 6 cap h sub 6 l Is the reaction endothermic or exothermic, and what is the enthalpy of reaction? Use Δ⁢H_rxn=∑(Δ⁢H_f_1p⁢r⁢o⁢d⁢u⁢c⁢t⁢s)−∑(Δ⁢H_f_1r⁢e⁢a⁢c⁢tan⁡t⁢s)

Use the formation-enthalpy equation: ΔH_rxn equals the sum for products minus the sum for reactants. The product, C₆H₆(l), has ΔH_f = 49.0 kJ/mol, while graphite and H₂ are elements in their standard states, so their formation enthalpies are 0. Thus ΔH_rxn = 49.0 − 0 = +49.0 kJ; a positive enthalpy change means the reaction is endothermic. The correct choice is “endothermic; ΔH_rxn = 49.0 kJ.”

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