A balanced chemical equation has an equal number of atoms of each element on both sides of the equation. This means that the number of atoms of each element in the reactants is equal to the number of atoms of each element in the products.

To check if an equation is balanced, you can:

1. Count the number of atoms of each element on both sides of the equation.

2. If the number of atoms of each element is the same on both sides, then the equation is balanced.

3. If the number of atoms of each element is not the same on both sides, then the equation is not balanced.

For example, let's consider the following equation:

```

2H2 + O2 -> 2H2O

```

This equation is balanced because there are two atoms of hydrogen on both sides of the equation, and there are two atoms of oxygen on both sides of the equation.

However, the following equation is not balanced:

```

H2 + O2 -> H2O

```

This equation is not balanced because there are two atoms of hydrogen on the left side of the equation, but only one atom of hydrogen on the right side of the equation.