# This is the equation for burning hydrogen in air: #2H_2 + O_2 -> 2H_2O. How many H and O atoms are shown on the left-hand side of the equation?

Sep 6, 2016

$2 {H}_{2} \left(g\right) + {O}_{2} \left(g\right) \rightarrow 2 {H}_{2} O \left(l\right)$.

Clearly, there are 4 hydrogen atoms.........

#### Explanation:

Clearly, there are 4 hydrogen atoms, but 2 hydrogen molecules, and 2 oxygen atoms, but 1 oxygen molecule on the left hand side of the equation.

And on the RHS, there must necessarily be 4 hydrogen atoms and 2 oxygen atoms, because it is a balanced chemical equation.

This illustrates the principle of stoichiometry, which reflects the conservation of mass. If you start with 10 g of reactant, AT MOST you can get 10 g of product.