Now children like to go to the fast food restaurant， as the name says，eating doesn't take much time.
化学键
H﹣H
O=O
H﹣O
键能（KJ/mol）
436
496
463
对于反应：2H2（g）+O2（g）=2H2O（g）△H=a KJ/mol，a的值为（ ）
