Question: How do you work out chemistry equations?

Varun Ramaswamy answered on 21 Apr 2020:

Ooh, that’s a nice question.

If you have H2 + O2, you cannot predict the answer. H2 and O2 can combine to form Water (H2O) or Hydrogen peroxide (H2O2), so unless they give you a few more hints about the substance thats being formed, you cannot fill up that blank.

BUT, if they give you a full equation : H2 + O2 –> H2O, you can work out the ratio of H2 and O2 that combine, by “balancing” this reaction.
The key to this is simple- just make sure you have an equal number of each species on the right and on the left.
H2 is the same on both sides, but for oxygen, I have O2 on the left and only O on the right.
Lets sort that out by making it 2H2O.
But wait, that means we have 2H2 on the right and only H2 on the left.
We can finally sort that out and the final equation would be:
2H2 + O2 –> 2H2O.

In short, you can’t predict the reaction always, you can only balance it.
And while balancing, the golden rule is: the number you start with is the number you should end with.

Hope this helps you out, and feel free to ask me if you have any queries 🙂