Why don't oil and water mix? - John Pollard

John Pollard：为什么油与水不能混合?

翻译人员: Jingwei Gu 校对人员: Ryan Miao

Why does salt dissolve in water but oil doesn't?

为什么盐可溶于水而油却不行呢？

Well, in a word, chemistry,

嗯，从一种角度来说，是化学作用，

but that's not very satisfying, is it?

但是这并不很令人信服，不是吗？

Well, the reason salt dissolves and oil does not

其实，盐可溶于水而油不能的原因

comes down to the two big reasons

可归结为一切事物与现象

why anything happens at all:

发生的两个根本原因：

energetics

力能学

and entropy.

和熵。

Energetics deals primarily

力能学主要讨论

with the attractive forces between things.

物体之间的引力。

When we look at oil or salt in water,

当我们观察水中的盐或油时，

we focus on the forces between particles

我们会在一个非常微小的尺度内

on a very, very, very small scale,

关注粒子之间的作用力，

the molecular level.

分子层级。

To give you a sense of this scale,

这个尺度究竟有多微小呢？

in one glass of water,

在一杯水里，

there are more molecules

分子的数量

than known stars in the universe.

比宇宙中已知的星星数量还要大。

Now, all of these molecules are in constant motion,

现在，所有这些分子都在做匀速运动，

moving, vibrating, and rotating.

移动、振动并且旋转。

What prevents almost all of those molecules

阻止了几乎所有的这些分子

from just flying out of the glass

从杯子里面飞出去的

are the attractive interactions between molecules.

是分子之间相吸引的相互作用力。

The strength of the interactions

在水与它自己之间，以及与其他物质之间

between water, itself, and other substances

相互作用力的力度

is what we mean when we say energetics.

就是我们所说的力能学的含义。

You can think of the water molecules engaging

你可以想象水分子

in a constant dance,

在始终如一地舞蹈着，

sort of like a square dance

有点像那种

where they constantly and randomly exchange partners.

经常且随机更换舞伴的方块舞。

Put simply, the ability for substances

简言之，物质与水之间，

to interact with water,

那种平衡于它们破坏

balanced with how they disrupt

水分子之间的相互作用的程度

how water interacts with itself,

的相互作用的能力，

plays an important role in explaining

在解释为什么有些物质可溶于水，

why certain things mix well into water

而另一些却不能时

and others don't.

扮演着重要的角色。

Entropy basically describes

熵基本描述了

the way things and energy can be arranged

建立在无规则运动基础上的

based on random motion.

物质与能量被组合的方式。

For example, think of the air in a room.

例如，想象一个房间里的空气。

Imagine all the different possible arrangements

想象一个空间里万亿个

in space for the trillions of particles

组成空气的分子

that make up the air.

所有可能的组合方式。

Some of those arrangments

其中一些组合方式

might have all the oxygen molecules over here

可能会将所有的氧分子置放在这一边

and all the nitrogen molecules over there,

而将所有氮分子置放在那一边，

separated.

使二者分离开来。

But far more of the possible arrangements

然而，更多可能的方式

have those molecules mixed up with one another.

是使这些分子彼此混合起来。

So, entropy favors mixing.

因此，熵倾向于讨论“混合”。

Energetics deals with attractive forces.

力能学则讨论引力。

And so, if attractive forces are present,

故而，如果引力存在，

the probability of some arrangements

一部分组合方式的可能性

can be enhanced,

便会被提高，

the ones where things are attracted to each other.

也就是那些物体彼此吸引的方式。

So, it is always the balance of these two things

所以，决定所发生的现象的

that determines what happens.

通常是这二者的平衡。

On the molecular level,

在分子层级上，

water is comprised of water molecules,

水是由水分子组成的，

made up of two hydrogen atoms and an oxygen atom.

水分子由两个氢原子和一个氧原子构成。

As liquid water, these molecules are engaged

作为液态水，这些分子从事着

in a constant and random square dance

恒定而随机的

that is called the hydrogen bonding network.

被称为“氢键网络”的“方块舞”。

Entropy favors keeping

熵倾向保持

the square dance going at all times.

这种“方块舞”一直进行。

There are always more ways

所有水分子

that all the water molecules can arrange

被组合成“方块舞”的方式

in a square dance,

总是会更多，

as compared to if the water molecules

如果和水分子被组合成“排舞”的方式

did a line dance.

比较的话。

So, the square dance constantly goes on.

因此，“方块舞”永恒地进行着。

So, what happens when you put salt in the water?

那么，当你把盐放进水里时会发生什么呢？

Well, on the molecular level,

嗯，在分子层级上，

salt is actually made up of two different ions,

盐其实是由两种不同的离子构成的，

chlorine and sodium,

氯离子和钠离子，

that are organized like a brick wall.

它们就像砖墙一样被组合起来。

They show up to the dance

它们以编队的形式作为一个大团体

as a big group in formation

出现在舞会上

and sit on the side at first,

并首先坐在了一边，

shy and a bit reluctant to break apart

害羞，并且有些不情愿去分离成

into individual ions to join the dance.

单独的离子来加入这场舞会。

But secretly, those shy dancers

但是这些腼腆的舞者

just want someone to ask them to join.

暗地里却希望有人让它们加入。

So, when a water randomly bumps into one of them

所以，当一个水分子偶然地碰到它们中的一个

and pulls them into the dance away from their group,

并且将它们推向舞会，远离它们的团体时，

they go.

它们就会去。

And once they go into the dance,

而且，只要它们加入了舞会，

they don't come back out.

就不会再回来了。

And in fact, the addition of the salt ions

事实上，盐的加入

adds more possible dance positions

使得“方块舞”的组合

in the square dance,

有了更多可能的形式，

so it is favored for them to stay dancing with water.

所以对它们来说与水共“舞”有好处。

Now, let's take oil.

现在，我们来说说油。

With oil, the molecules are sort of interested

油分子对与水共“舞”

in dancing with water,

还是有点感兴趣的，

so entropy favors them joining the dance.

所以熵偏向于让它们加入舞会。

The problem is that oil molecules

而问题在于油分子

are wearing gigantic ballgowns,

都穿着巨大的长礼服，

and they're way bigger than water molecules.

而且它们比水分子大得多。

So, when an oil molecule gets pulled in,

所以，当一个油分子加入舞会时，

their size is really disruptive to the dance

它的身量简直对舞会具有破坏性

and the random exchange of partners

而且，水所从事的

that the waters engage in,

随机更换舞伴的行为，

a very important part of the dance.

是舞会的一个重要部分。

In addition, they are not great dancers.

此外，它们也不是杰出的舞者。

The water molecules try to engage

水分子试图让油分子

the oil molecules in the dance,

参与到舞会当中来，

but they just keep bumping into their dresses

但是它们总是碰到它们的礼服

and taking up all the room on the dance floor.

并且占掉了舞池里所有的空间。

There are way more ways the waters can dance

当油离开舞池时

when the oil gets off the floor,

水跳舞的方式就多了许多，

so the waters squeeze out the oil,

所以水把油挤了出去，

pushing it back to the bench with the others.

把它推回了其他油分子一起坐着的长凳子上。

Pretty soon, when a large number of oils

不一会儿，当一大群油分子

have been squeezed over to the side,

都被挤到一边时，

they band together to commiserate

它们就会聚到一起，并且遗憾地叹息

about how unfair the waters are being

水是多么的不公平

and stick together as a group.

然后粘在一起成为一个团体。

So, it is this combination

因此，就是这种

of the interactions between molecules

当分子在无规则运动时，它们之间

and the configurations available to them

的相互作用的结合

when they're moving randomly

以及对它们来说可能实现的构造

that dictates whether they mix.

决定了它们是否能够混合。

In other words, water and oil don't mix

换一句话说，油和水不能混合的原因

because they just don't make great dance partners.

就是因为它们组不成完美的舞伴。