Final answer:
Breaking up the lumps in baking soda increases the surface area of the particles, allowing for more efficient chemical reactions.
Step-by-step explanation:
The reason it is important to break up the lumps in baking soda is because it increases the surface area of the baking soda particles. When a reaction occurs, the particles need to come into contact with each other in order to react. Breaking up the lumps allows for more contact between the baking soda and the reactant, resulting in a faster and more efficient chemical reaction.