英語聽力文摘462 食鹽大戰(zhàn)冰塊

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Salt vs. Ice

食鹽大戰(zhàn)冰塊

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 equilibrium 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 molecules are replaced by salt. Since there are now fewer liquid water molecules to be captured and frozen 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：為什么食鹽能讓冰塊融化?

D：是因為食鹽將水的熔點和冰點降低了。

Y：等一下，我不明白。這就意味著食鹽讓冰的溫度變得更低嗎?

D：我解釋一下。純凈水的冰點是32華氏度，對吧?這個溫度既是冰點也是熔點。

Y：也就是說，水的冰點就是結(jié)冰和融化的平衡。

D：是的。在冰上灑鹽擾亂了這種平衡。

Y：怎么打亂的呢?

D：鹽溶解在水中，就是說一部分水分子被鹽取代了。既然結(jié)冰的液態(tài)水分子減少了，冰點自然降低了。

Y：我明白了。水的熔點不變，融化的水分子比結(jié)冰的多，所以冰塊就融化了。

D：對。

Y：很有趣。

D：其實，任何溶于水的物質(zhì)都可以使冰融化。把糖灑在冰上，冰也會融化。但是我想也許由于鹽比較便宜，所以經(jīng)常被使用。