从宏观来看化学变化的本质是有新物质生成。从微观角度来看，下列变化不能说明发生了化学变化的是 ( )。
A．变化时有电子的得失或共用电子对的形成
B．变化过程中有化学键的断裂和形成
C．变化时释放出能量
D．变化前后原子的种类和数目没有改变，分子种类增加了
答案：C
某些物理变化也能释放能量，如浓H2SO4、NaOH等溶于水放出热量，白炽灯工作时发光发热等。
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2. Sorry, I don't know where the post office is. I am a _______. 3. As soon as his first novel was published, he earned a _______. 4. _______ have very long back legs for jumping. 5. The old couple _______ their living by collecting and selling used plastic bottles. 6. X is often used to represent an _______ number. 7. After the lunch we parted, so I didn't know what happened to him _______. 8. I get a low salary so sometimes I work _______ to earn more. 9. He fastened the belt _______ around his waist. 10. Beethoven, a great German _______, lived between 1770 and 1827. |