What triggers a chemical reaction? - Kareem Jarrah

翻译人员: Claire Zhang 校对人员: Luyao Zou

You know how sometimes you go to bake a cake

你想去烘培一个蛋糕

but your bananas have all gone rotten,

但是发现香蕉都腐烂掉了

your utensils have rusted,

餐具也都生锈了

you trip and pour all of your baking soda into the vinegar jug,

你不小心摔了一跤 把所有的烘焙粉都倒在了醋瓶子里面

and then your oven explodes?

然后你的烤箱就爆炸了！

My friend, you and your chemical reactions have fallen victim to enthalpy and entropy

朋友们， 你和你的化学反应都成为了焓和熵的受害者

and, boy, are they forces to be reckoned with.

孩子，这是可以预料到的吗？

Now, your reactants are all products.

现在，你的反应物都成了产物

So, what are these "E" words, and what's their big idea?

所以，这些“E”是什么，他们又代表了什么

Let's start with enthalpy,

让我们先从焓开始

an increase or decrease of energy during a chemical reaction.

它是在化学反应过程中 能量的增加或者减少

Every molecule has a certain amount of chemical potential energy

每一个分子都有一定的化学势能

stored within the bonds between its atoms.

存储在它原子之间的化学键中

Chemicals with more energy are less stable,

能量越高的化学物质越不稳定

and thus, more likely to react.

因此就越有可能发生反应

Let's visualize the energy flow in a reaction,

让我们通过一轮疯狂的高尔夫

the combustion of hydrogen and oxygen, by playing a round of crazy golf.

来看看在氢氧燃烧反应中 能量是怎么流动的吧

Our goal is to get a ball, the reactant, up a small rise

我们的目标是将这个球， 反应物，上升一些

and down the other much steeper slope.

然后向另一个陡峭的斜坡下滚

Where the hill goes up, we need to add energy to the ball,

在上坡的时候，我们需要给球输入能量

and where it goes down, the ball releases energy into its surroundings.

当它下滚时， 它会向周围释放能量

The hole represents the product, or result of the reaction.

而洞则代表了产物， 或者说反应的结果

When the reaction period ends, the ball is inside the hole,

当反应周期结束时， 球会掉入洞中

and we have our product: water.

然后我们将得到产物——水

This, like when our oven exploded, is an exothermic reaction,

这，像刚才说的微波炉爆炸一样， 是放热反应

meaning that the chemical's final energy is less than its starting energy,

指的是化学反应后的能量会比开始前的少

and the difference has been added to the surrounding environment

而这些差量会以光或者热量的形式

as light and heat.

释放到周围的环境中

We can also play out the opposite type of reaction,

当然，还有另一种相反的反应

an endothermic reaction,

吸热反应

where the final energy is greater than the starting energy.

指的是最后的能量比反应开始前要多

That's what we were trying to achieve by baking our cake.

在烘焙蛋糕时产生的就是这种反应

The added heat from the oven would change the chemical structure

烤箱中升高的温度会改变

of the proteins in the eggs and various compounds in the butter.

鸡蛋中蛋白质和黄油中各种物质的化学结构

So that's enthalpy.

这便是焓

As you might suspect,

你可能会想

exothermic reactions are more likely to happen than endothermic ones

放热反应比吸热反应更容易发生

because they require less energy to occur.

因为相比之下，它需要的能量更少

But there's another independent factor that can make reactions happen:

但还有另一个独立的因素， 也可以让化学反应发生：

entropy.

熵

Entropy measures a chemical's randomness.

熵衡量了化学物质的混乱程度

Here's an enormous pyramid of golf balls.

这里有一个用高尔夫球堆成的巨大金字塔

Its ordered structure means it has low entropy.

它结构规整， 意味着较低的熵

However, when it collapses, we have chaos everywhere,

然而，当它倒塌时，就会混乱一片

balls bouncing high and wide.

球弹跳的到处都是。

So much so that some even go over the hill.

多到有些球直接翻过了山坡

This shift to instability, or higher entropy,

这种转向不稳定状态 或者说较高的熵的趋势

can allow reactions to happen.

能让反应发生

As with the golf balls, in actual chemicals

和高尔夫球一样， 真实的化学物质中

this transition from structure to disorder gets some reactants past the hump

这种从有次序到无次序的转变 会使某些反应物越过能垒

and lets them start a reaction.

使它们产生反应

You can see both enthalpy and entropy at play

可以看到，在你点燃营火准备煮晚餐时， 焓和熵同时起了作用

when you go to light a campfire to cook dinner.

Your match adds enough energy

你的火柴提供了足够的能量

to activate the exothermic reaction of combustion,

启动放热的燃烧反应

converting the high-energy combustible material in the wood

进而转化木头中的 高能量可燃物质

to lower energy carbon dioxide and water.

成能量低的二氧化碳和水。

Entropy also increases and helps the reaction along

熵也会增加以及帮助反应持续进行

because the neat, organized log of wood

这是因为排列整齐，有条理的木头

is now converted into randomly moving water vapor and carbon dioxide.

现在转化为自由移动的 水蒸汽和二氧化碳

The energy shed by this exothermic reaction

这些放热反应放出的能量

powers the endothermic reaction of cooking your dinner.

正好提供煮晚餐的吸热反应的热能

Bon appétit!

祝你好胃口!