题目

In the mid 1990’s, people started doing business on the Internet. At that time, there were two kinds of companies. First, there were traditional companies. They sold things in stores. Then there were Internet companies. They didn’t have a store, and they only sold things on the Net.    Traditional companies didn’t want to lose any business. Quickly they made their own websites and began selling things on the Net. These are the so-called “brick and click” companies. Many stores are made of brick. And you click on your mouse to buy things with your computer. That’s where the name 已知如果反应物的总能量大于生成物的总能量，那么该反应为放热反应，反之为吸热反应．请你列举出三个放热反应的例子，用离子方程式表示：①____________________________________________________________ ②____________________________________________________________ ③____________________________________________________________ 再列举三个吸热反应的例子，用化学方程式表示： ①____________________________________________________________ ②____________________________________________________________ ③____________________________________________________________