7.已知:101kPa时的辛烷的燃烧热为5518kJ·mol-1,强酸与强碱在稀溶液中发生反应时的中和热57.3kJ·mol-1,则下列热化学方程式书写正确的是( )
①C8H18(l)+25/2O2(g) 8CO2(g)+9H2O(l);△H=+5518kJ·mol-1
②C8H18(l)+25/2O2(g) 8CO2(g)+9H2O(l);△H=-5518kJ·mol-1
③H++OH- H2O;△H=-57.3kJ·mol-1
④NaOH(aq)+1/2H2SO4(aq) 1/2Na2SO4(aq)+H2O(l);△H=+57.3kJ·mol-1
A.①③ B.②③ C.②④ D.只有②