6.2 - Rate Factors & Collision Theory

Factors that affect reaction rate

• Temperature - Increasing the temperature increases the rate.
• Concentration and pressure - Increasing the concentration of a reactant in solution, or increasing the pressure of a reacting gas, increases the rate.
• Surface area - Increasing the surface area of a solid reactant (by breaking it into smaller pieces or using a powder) increases the rate.
• Catalyst - Adding a catalyst increases the rate.

Catalysts

• A catalyst is a substance that speeds up a chemical reaction without being used up in the process.
• It remains chemically unchanged, so its mass is the same at the start and end of the reaction.
• A catalyst doesn't appear in the balanced equation for the reaction.
• Enzymes are biological catalysts.

Example - Decomposing hydrogen peroxide

Hydrogen peroxide decomposes very slowly on its own. Adding solid manganese(IV) oxide speeds up the reaction:

hydrogen peroxide → water + oxygen

2H₂O₂(aq) → 2H₂O(l) + O₂(g)