问题 选择题

化学用语是学习化学的重要工具。下列用来表示物质变化的化学用语中,错误的是

A.钢铁腐蚀时可能发生的正极反应:2H2O+ O2+ 4e=4OH

B.明矾水解的离子方程式: Al3++3 H2OAl(OH)3+3H+

C.少量氢氧化钙溶液与碳酸氢钠溶液混合:OH+ HCO3=H2O+ CO32

D.表示氢气燃烧的热化学方程式2H2(g)+O2(g)=2H2O(l);△H=+571.6kJ·mol1

答案

CD

C不正确,应该生成碳酸钙沉淀。燃烧热是在一定条件下,1mol可燃物完全燃烧生成稳定的氧化物时所放出的热量,D不正确,AB都是正确的,答案选CD。

单项选择题
单项选择题

The fridge is considered a necessity. It has been so since the 1960s when packaged food first appeared with the label: "store in the refrigerator. "

In my fridgeless fifties childhood, I was fed well and healthy. The milkman came daily, the grocer, the butcher, the baker, and the ice cream man delivered two or three times a week. The Sunday meat would last until Wednesday and surplus bread and milk became all kinds of cakes. Nothing was wasted, and we were never troubled by rotten food. Thirty years on, food deliveries have ceased, fresh vegetables are almost unobtainable in the country.

The invention of the fridge contributed comparatively little to the art of food preservation. A vast way of well tried techniques already existed—natural cooling, drying, smoking, salting, sugaring, bottling…

What refrigeration did promote was marketing—marketing hardware and electricity, marketing soft drinks, marketing dead bodies of animals around the globe in search of a good price.

Consequently, most of the world’s fridges are to be found, not in the tropics where they might prove useful, but in the wealthy countries with mild temperatures where they are climatically almost unnecessary. Every winter, millions of fridges hum away continuously, and at vast expense, busily maintaining an artificially cooled space inside an artificially heated house—while outside, nature provides the desired temperature free of charge.

The fridge’s effect upon the environment has been evident, while its contribution to human happiness has been insignificant. If you don’t believe me, try it yourself, invest in a food cabinet and turn off your fridge next winter. You may miss the hamburgers, but at least you’ll get rid of that terrible hum.

Why does the author say that nothing was wasted before the invention of fridges().

A.People would not buy more food than was necessary.

B.Food was delivered to people two or three times a week.

C.Food was sold fresh and did not get rotten easily.

D.People had effective ways to preserve their food.