What would happen if you added more than 5 mL of H2O2 to the 5 mL of yeast solution?

The hydrogen peroxide would dissociate down into oxygen and water.

Explanation:

The hydrogen peroxide dissociates into oxygen and water.

2H₂O₂ → 2H₂O + O₂

The yeast comprises an enzyme known as catalase that catalyzes the reaction. Greater the concentration of the catalyst supplemented, the faster will be the decomposition of the hydrogen peroxide. Therefore, if one adds more than 5 milliliters of H₂O₂ to the yeast solution, the dissociation would take place at a quicker rate, and the bubbles and the accompanying fizz would be in a higher amount.

The yeast breaks down the hydrogen peroxide (H2O2) into oxygen and water.