Question

`H_2(g) + Cl_2(g) -> 2HCl(g)+`. If 2 mol of hydrogen gas are mixed with 4 mol of chlorine gas, how many moles of hydrogen chloride will be produced?

Answer 1

4 moles of HCl are produced

Explanation:

The ratio at which the compounds react with each other are displayed in a chemical reaction as the numbers in front of the compounds. For example in this reaction:

1 `H_2` molecule reacts with 1 `Cl_2` molecule
Forming
2 `HCl` molecules.

In chemistry moles are used as a handy number of a certain amount of stuff. You can compare this to a dozen eggs, which is always 12. In the same way 1 mol is the number `6.022*10^(23)`. This number tells us how many particles there are. So in 1 mol there are `6.022*10^(23)` particles. This number is also referred to as the constant of Avogadro.

In the question the amount of moles for `H_2` and for `Cl_2` are given. We have to calculate how much `HCl` is produced with both these values. Therefore 2 calculations needs to be done.

Because moles just tells us something about the amount of particles we can use the ratio of the reaction to calculate how many `HCl` will be produced.

We start of with the 2 moles of hydrogen gas. We know the following now:
1 mole of `H_2` gives 2 moles of `HCl`
Therefore
2 moles of `H_2` gives 4 moles of `HCl`

Now this same calculation can be done for the `Cl_2`:
1 mole of `Cl_2` reacts to 2 moles of `HCl`, therefore
4 moles of `Cl_2` reacts to 8 moles of `HCl`.

Now we see we have 2 different amount of moles for `HCl` and the question now is which one should we use?
We must now look at which one of above reactions can occur? So for the 2 moles of `H_2`, we can calculate with the ratio that:
2 moles of `H_2` reacts with 2 moles of `Cl_2`.
We do have 2 moles of `Cl_2` available!

Let's see the other one
4 moles of `Cl_2` reacts with 4 moles of `H_2`
But we do not have 4 moles of `H_2`!!

Therefore we can only make 4 moles of `HCl` instead of 8 moles.

This situation can be stated as following: The `Cl_2` is abundant.