搜题请搜索小程序“爱下问搜题”
问题 选择题

下列变化过程，属于放热过程的是（　　）

①液态水变成水蒸气；  ②酸碱中和反应；  ③浓H2SO4稀释；  ④固体氢氧化钠溶于水；  ⑤H2在Cl2中燃烧；

⑥弱酸电离；  ⑦NH4Cl晶体与Ba（OH）2•8H2O混合搅拌．

A．①③⑤

B．①⑥⑦

C．②③④

D．②③④⑤

答案

①液态水变成水蒸气，是物理变化中的汽化，是吸热过程，故①错误；

②酸碱中和反应，是典型的放热反应，是放热过程，故②正确；

③浓H2SO4稀释，是物理变化，是放热过程，故③正确；

④固体氢氧化钠溶于水，是物理变化，是放热过程，故④正确；

⑤H2在Cl2中燃烧，所有的物质燃烧，是典型的放热反应，是放热过程，故⑤正确；

⑥弱酸电离，是化学变化中的吸热反应，是吸热过程，故⑥错误；

⑦NH4Cl晶体与Ba（OH）2•8H2O混合搅拌，是典型的吸热反应，是吸热过程，故⑦错误；

故选D．

填空题

Window 98采用层次性的模块化结构，它主要由用户界面(或称为用户接口工具)和【 】组成。
查看答案
单项选择题

Letter A

Dear Rose,

I like your programmes very much. I’m now writing to ask you something about American social customs. My American friends want me to join them in their dinner party. I am very happy and have decided to go, but I’m a little worried about it, too. The social customs in my country are very different from here, so I’m afraid of making mistakes.

Should I bring a present, such as sweets or flowers Should I arrive on time or a little late At the dinner table, how can I know which fork or knife to use How can I let the family know that I’m thankful for their kindness

Wang Lin

Letter B

Dear Wang Lin,

It’s a good idea to bring a small present when you go to a dinner party. Flowers are always nice, or you may bring a bottle of wine if you know that your friends drink it.

You should arrive on time or five to ten minutes late. Don’t get there early. If you’re going to be more than fifteen minutes late, you should call and tell them.

Try. to be free at the dinner table. If you don’t know about choosing the right fork or knife, just watch the other people, and follow them. If you still have no idea of what to do, ask the person next to you.

If you like the food, say so. Of course, you’ll thank them for the meal and for their kindness. It’s also a good idea to send a thank you card the day after.

Rose

Rose is possibly （）.

A．a good housewife

B．a TV hostess

C．a member of the dinner party

D．a friend of Wang Lin’s
查看答案