化学是关于最小的物体构成其他更大的物体，以及当它们变化时会发生什么的一门学科。

Chemistry is about the smallest things that other bigger things are made of, and what happens when they change.

youdao

,我是一个系统，其余的是周围的环境,那么当我在做所有的化学反应,去四处移动我的手臂的时候,什么量是常数？

What's the one function of state that's constant when I'm doing all my chemical reactions to move my arms around?

youdao

你有你的技能，你是个厨师、化学家或者慈善工作者，没有什么能改变这个事实。

You have your capabilities; you may be a cook or a chemist or a charity worker and nothing can take that away.

youdao

So we can think about something I mentioned last time, which is when we're thinking about chemistry and what's really interesting in terms of chemical reactions, it's mostly valence electrons we're talking about, those are the ones that tend to be involved in chemical reactions.

我们可以考虑一下我上次提到过的一件事，那就是如果我们讨论化学,以及什么是化学反应中,真正令人感兴趣的东西，我们讨论的几乎都是价电子，它们才是在化学反应中,真正起作用的部分。

麻省理工公开课 - 化学原理课程节选

It depends on the class, like, organic chemistry, for instance, is always open book, open notes.

这要看是什么科目，例如说有机化学总是开卷考试，可以看笔记。

考试应该这么准备 - SpeakingMax英语口语达人

What is it when you run a chemical reaction under ordinary circumstances, what's constant?

如果你在通常的环境下进行化学实验,那么这些条件是什么？什么保持常数？

麻省理工公开课 - 热力学与动力学课程节选