如图是778K时N2与H2反应过程中能量变化的曲线图．下列叙述正确的是（ ）
A．此反应N2+3H2⇌2NH3为放热反应
B．b曲线是加入催化剂时的能量变化曲线
C．加入催化剂，该化学反应的△H变大
D．加入催化剂可增大正反应速率，逆反应速率不变
A、由图象可知，反应物的能量大于生成物的能量，所以该反应为放热反应，故A正确；
B、催化剂能改变反应的路径，使发生反应所需的活化能降低，但不改变化学平衡，反应的热效应不变，故图象中的b曲线是加入正催化剂时的能量变化曲线，故B正确；
C、催化剂能改变反应的路径，使发生反应所需的活化能降低，但不改变化学平衡，反应的热效应不变，故C错误；
D、催化剂能改变反应的路径，使发生反应所需的活化能降低，正反应速率和逆反应速率都增大，故D错误；
故选AB．
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