An equation is said to be balanced when the number of atoms of each element is the same on both sides of the equation. To determine if an equation is balanced, follow these steps:

1. Count the number of atoms of each element on the left side of the equation.

2. Count the number of atoms of each element on the right side of the equation.

3. Compare the number of atoms of each element on both sides of the equation.

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

For example, consider the following equation:

$$A + 2B → C + D$$

1. On the left side of the equation, there are 1 atom of A and 2 atoms of B.

2. On the right side of the equation, there are 1 atom of C and 1 atom of D.

3. The number of atoms of A is not the same on both sides, so the equation is not balanced.

4. To balance the equation, we need to add a coefficient in front of C or D until the number of atoms of A is the same on both sides. By adding a coefficient of 2 in front of C, we obtain the following balanced equation:

$$A + 2B → 2C + D$$

Now, there are 1 atom of A on both sides and 2 atoms of B on both sides. The equation is balanced.