①2H 2O(g)=2H 2(g)+O 2(g)△H 1;
②H 2(g)+Cl(g)=2HCl(g)△H 2 ;
③2Cl 2(g)+2H 2O(g)=4HCl(g)+O 2(g)△H 3;
则反应③=①+2×②,
由盖斯定律可知,
△H 3=△H 1+2△H 2,
故选A.
①2H 2O(g)=2H 2(g)+O 2(g)△H 1;
②H 2(g)+Cl(g)=2HCl(g)△H 2 ;
③2Cl 2(g)+2H 2O(g)=4HCl(g)+O 2(g)△H 3;
则反应③=①+2×②,
由盖斯定律可知,
△H 3=△H 1+2△H 2,
故选A.