已知热化学方程式:① C2H2(g) +52O2(g) == 2CO2(g)+H2O(l) ΔH1=-1301.0 kJ•mol-1② C(s)+ O2(g) == CO2(g) △H2=-393.5 kJ•mol-1③ H2(g)+ 12O2(g) == H2O(1) △H3 = -285.8 kJ·mol-1则反应④ 2C(s)+ H2(g) == C2H2(g)的△H为( )
太阳直射南回归线的这一天,是北半球的( )