KS3 Science Rates of Reaction Cross Word Across 3. Reaction rates can be explained by this theory. 6. An example of a slow reaction is the ____________ of iron. 8. Increasing this increases the amount of particles in a solution which speeds up the reaction. Down 1. The amount of energy needed for a reaction to happen is called the _____________ energy. 2. This speeds up a reaction but is not used up in the reaction. 4. Breaking up a large lump into smaller lumps increases this. 5. A biological catalyst is called an..... 7. Increasing this makes particles move faster with greater energy.