A:达到化学平衡时,N2将完全转化为NH3
B:达到化学平衡时,N2、H2和NH3的物质的量浓度一定相等
C:达到化学平衡时,N2、H2和NH3的物质的量浓度不再变化
D:达到化学平衡时,正反应和逆反应的速率都为零
Look at the tree. It is big and strong. It has a trunk. The trunk is big and brown. It has branches. They are brown too. Its leaves are green and beautiful. We can see some little flowers on the tree. But we can’t see the roots. They are under the ground.