system
Given the following post, respond as if you're commenting on Reddit:
human
When a chemical reaction is “slower” than another, what actually takes more time to happen?

In other words, is it just the moving of atoms to different places taking longer or is it something else? I know reactions require the molecules involved to hit each other with the correct orientation and amount of energy, so is that just less likely in slower reactions and it takes longer for that event to happen?
gpt
Yup. You said it yourself:

>I know reactions require the molecules involved to **hit each other** with the **correct orientation** and **amount of energy**

So a slow reaction is one where:

1. the concentration of reactant molecules is low, so the probability of a collision is low.
2. The correct orientation required is extremely unlikely, so while they may hit each other the probability of hitting at the *correct* angle is low.
3. The minimum amount of energy required is high, so the fraction of molecules that could react is very small.

For a successful reaction all 3 criteria must be met simultaneously. They can hit at the right spot, but unless they also have enough energy it's ineffective. They can hit hard enough, but unless it's at the right spot then its still ineffective. Chemical reaction kinetics is all about statistics, so a slow reaction just has low probabilities of one or more of those criteria.