题目

在25℃、100 kPa时，已知：①2H2O(g) = O2(g)+2H2(g) ΔH1②Cl2(g)+H2(g) = 2HCl(g) ΔH2 ③2Cl2(g)+2H2O(g) = 4HCl(g)+O2(g) ΔH3则ΔH3与ΔH1、ΔH2间的关系正确的是 （）A.ΔH3 = ΔH1＋2ΔH2 B.ΔH3 = ΔH1＋ΔH2C.ΔH3 = ΔH1—2ΔH2 D.ΔH3 = ΔH1—ΔH2 答案：【答案】A【解析】已知：2H2O(g)=O2(g)＋2H2(g) ΔH1 ①Cl2(g)＋H2(g)=2HCl(g) ΔH2 ②2Cl2(g)＋2H2O(g)=4HCl(g)＋O2(g) ΔH3 ③根据盖斯定律，将反应①＋反应②×2即可求得反应③，因此有ΔH3＝ΔH1＋2ΔH2。答案选A。 ________ is known to everybody that the moon travels round the earth once every month． [　　] A．That B．It C．As D．What