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Dr. Dolhun had hydrogen peroxide in the plastic bottle
Dolhun博士的塑料瓶中装有过氧化氢
Then he added a catalyst, some manganese dioxide
然后他加入了一种催化剂，二氧化锰
or Mn02
也就是MnO2
and got plume of water vapor
最后瓶中喷出一缕蒸汽
So let's talk about how catalyst works
我们来谈谈催化剂是如何工作的
I'm going to draw a potential energy diagram for this reaction
我将为该反应画一个势能图
So here's my potential energy diagram
这是我的势能图
So we have potential energy on the y-axis
势能位于纵轴上
and the reaction coordinate or time on the x-axis
而反应坐标，或者说时间，位于横轴上
Reactants are starting at this amount of energy
反应物最开始有这么多能量
and the products have this amount
而产物有这么多能量
Here Ea, that's the activation energy
这里Ea表示活化能
It's the amount of energy you need to add to the reactants
需要给反应物提供这么多能量
to make the reaction go
反应才会发生
And ΔH
而ΔH
that's the amount of energy that's released when the reaction happens
是反应发生时所释放出来能量的量
Now let's see what happens when I add a catalyst
再看看加入催化剂时会怎样
With a catalyst, my activation energy is a lot lower
使用催化剂时，活化能大幅降低
And even a small reduction in activation energy
哪怕活化能只降低少许
can make the reaction go thousands of times faster than it normally would
反应也能比通常情况下快数千倍
but notice that regardless of whether or not you have a catalyst
但要注意，不管加不加催化剂
the ΔH, the amount of energy released in the reaction, doesn't change
反应中所释放能量的量ΔH是不会变化的
So the catalyst only speeds up the reaction
催化剂只加速反应速度
It doesn't change the amount of energy released
不会改变所释放能量的量
Now take a look at this
看看这个
Notice the size of the bottles
注意瓶子的大小
These are very exothermic reactions
这些是放热很多的反应
The bottle basically shrunk down to a very very tiny size
同对照组的瓶子比起来，
compared to the control bottles
瓶子缩小了很多
So as you can see, the catalyzed reaction releases so much heat
可以看到，催化反应释放了很多热量
that it actually melt the bottles and makes them smaller
让瓶子开始熔化，变小
Also the catalyst itself remains unchanged by the reaction
另外，催化剂本身在反应中不会变化
and designing catalyst is actually a key subfield of chemistry
而设计催化剂也是化学中的一个重要领域
MIT's Richard Schrock
MIT的理查德·施罗克
won the Nobel Prize working in this field
就因在该领域中的研究获得过诺贝尔奖
And remember how we used H2O2 on our cuts?
还记得将H2O2涂到伤口的情况吗
Well, we have an enzyme in our bodies called catalase
我们人体内有一种酶叫过氧化氢酶
that does the same thing as the manganese dioxide that Dr. Dolhun used
其作用同Dolhun博士所使用的二氧化锰相同
That's why when you put hydrogen peroxide on a cut
因此将过氧化氢涂到伤口上时
you see fizzing and bubbles
会产生嘶嘶声和泡泡
The catalase in your blood is breaking down the hydrogen peroxide
这表示血液中的过氧化氢酶正在分解过氧化氢
And according to recent studies
根据最新研究
low levels of catalase may play a role in the greying process of human hair
低过氧化氢酶水平在头发变白过程中扮演了重要角色
If catalase levels are low
过氧化氢酶水平偏低时
it can't break down all the hydrogen peroxide in the blood
血液中的过氧化氢就不能被完全分解
and that extra H2O2 starts to bleach your hair from the inside out
残留的H2O2会从内部将头发漂白
So to wrap up, catalyst don't change the products of the reaction
总结一下，催化剂不会改变反应的产物
or how much heat is released or absorbed
也不会改变反应释放或吸收的热量
They only change the time it takes for the reaction to finish
催化剂只会改变反应完成所需的时间
Alright that's it for me today
今天就到这里
I'll see you next time
我们下次再见
