Question

How many grams of H2O will be formed when 26.5 g H2 reacts with 26.5 g of O2 according to the reaction:
2H2 + O2 → 2H2O

Answer 1

We have the equation

2H₂ + O₂ → 2H₂O.

Calculate how many moles of H₂ and O₂ there are in 26.5 g of each substance:

$$n_{H_2}=\frac{m}{\Mu_{H_2}}=\frac{26.5}{2}=13.3\text{ mol},\\ \space\\ n_{O_2}=\frac{m}{\Mu_{O_2}}=\frac{26.5}{32}=0.828\text{ mol}.$$

We will calculate the reaction by oxygen because it has the smallest amount of substance. The amount of substance of water required is

$$n_{H_2O}=2n_{O_2},\\ \space \\m_{H_2O}=n_{H_2O}\cdot\Mu_{H_2O}=\\=2n_{O_2}\cdot\Mu_{H_2O}=\\ =2\cdot0.828\cdot18=29.8\text{ g}.$$