Welcome to balancing redox reactions. Today we'll balance the decomposition of hydrogen peroxide into water and oxygen gas. This is a special type of redox reaction called disproportionation, where the same element is both oxidized and reduced.
The first step in balancing any redox reaction is to identify the oxidation states. In hydrogen peroxide, oxygen has an oxidation state of negative one. In water, oxygen is negative two. In oxygen gas, oxygen is zero. Notice that oxygen goes from negative one to both negative two and zero, confirming this is a disproportionation reaction.
Next, we count the oxygen atoms on each side of the equation. On the left, hydrogen peroxide has 2 oxygen atoms. On the right, water has 1 oxygen atom and oxygen gas has 2 oxygen atoms, totaling 3. Since we have 2 on the left and 3 on the right, the equation is not balanced.
Now let's add coefficients to balance the equation. If we put a coefficient of 2 in front of hydrogen peroxide, we get 4 oxygen atoms on the left. To balance this, we need 2 water molecules plus 1 oxygen molecule on the right, which also gives us 4 oxygen atoms. The balanced equation is 2 H 2 O 2 equals 2 H 2 O plus O 2.
To summarize, we successfully balanced the redox reaction by first identifying oxidation states, recognizing the disproportionation pattern, and systematically adding coefficients. The final balanced equation is 2 H 2 O 2 equals 2 H 2 O plus O 2, with both oxygen and hydrogen atoms properly balanced.