C4h4 (g) + 2 h2 (g) --> c4h8 (g) combustion reactions involve reacting a substance with oxygen. when compounds containing carbon and hydrogen are combusted, carbon dioxide and water are the products. using the enthalpies of combustion for c4h4 (-2341 kj/mol), c4h8 (-2755 kj/'mol), and h2 (-286 kj/mol), calculate the change in heat for this reaction.