已知:H2(g)+ O 2(g)====H2O(g),反应过程中能量变化如下图,问:
(1)a、b、c分别代表什么意义?
a._____________________________________________________________________________;
b._____________________________________________________________________________;
c.
_____________________________________________________________________________。
(2)该反应是放热还是吸热?___________。ΔH大于零还是小于零?___________。