英语听力文摘 English Digest 462、食盐大战冰块

Salt vs. Ice
食盐大战冰块

Y: Why does salt melt ice?
D: It lowers the melting and freezing point of water. 

Y: Oh,OK.Wait,I don't get it. Doesn't that mean the salt make ice colder?
D: Let me explain.Pure water freezes at thirty-two degrees Fahrenheit,right? At that temperature we can say that the rate of freezing is the same as the rate of melting.

Y: So in other words, at water’s freezing point there’s a sort of equilibrium¹ between freezing and melting. 
D: Right.Throwing salt on ice upsets the balance.

Y: Upsets it how?
D: The salt dissolves into the liquid water, which means that some of the water molecules² are replaced by salt. Since there are now fewer liquid water molecules to be captured and frozen³ by the ice, the rate of freezing drops.

Y: I think I get it.And Since the rate of melting stays the same, there’s more melting going on than freezing. And so the ice melts.
D:Right.

Y: Interesting.
D: In fact, anything that dissolves in water will do the trick. You could pour sugar on ice and it will melt. But I guess since salt is cheaper it’s used more often.

Y：为什么食盐能让冰块融化？
D：是因为食盐将水的熔点和冰点降低了。
Y：等一下，我不明白。这就意味着食盐让冰的温度变得更低吗？
D：我解释一下。纯净水的冰点是32华氏度，对吧？这个温度既是冰点也是熔点。
Y：也就是说，水的冰点就是结冰和融化的平衡。
D：是的。在冰上洒盐扰乱了这种平衡。
Y：怎么打乱的呢？
D：盐溶解在水中，就是说一部分水分子被盐取代了。既然结冰的液态水分子减少了，冰点自然降低了。
Y：我明白了。水的熔点不变，融化的水分子比结冰的多，所以冰块就融化了。
D：对。
Y：很有趣。
D：其实，任何溶于水的物质都可以使冰融化。把糖洒在冰上，冰也会融化。但是我想也许由于盐比较便宜，所以经常被使用。

 

1 equilibrium   

n.平衡，均衡，相称，均势，平静

参考例句：

• Change in the world around us disturbs our inner equilibrium.我们周围世界的变化扰乱了我们内心的平静。
• This is best expressed in the form of an equilibrium constant.这最好用平衡常数的形式来表示。

2 molecules   

分子( molecule的名词复数 )

参考例句：

• The structure of molecules can be seen under an electron microscope. 分子的结构可在电子显微镜下观察到。
• Inside the reactor the large molecules are cracked into smaller molecules. 在反应堆里，大分子裂变为小分子。

3 frozen   

adj.冻结的，冰冻的

参考例句：

• He was frozen to death on a snowing night.在一个风雪的晚上，他被冻死了。
• The weather is cold and the ground is frozen.天寒地冻。