Rates of Reaction
Factors affecting how fast reactions occur and collision theory
Rate of reaction = how quickly reactants are converted to products. Measured by amount of product formed (or reactant used) per unit time.
Collision theory: Reactions occur when particles collide with **sufficient energy** (activation energy). More successful collisions = faster rate.
Factors affecting rate:
- Temperature — higher T → particles move faster → more frequent AND more energetic collisions → faster rate
- Concentration (or pressure for gases) — more particles per volume → more frequent collisions
- Surface area — smaller particles expose more surface → more collisions possible
- Catalyst — provides alternative pathway with lower activation energy → more particles have enough energy. Not consumed.
Measuring rate:
- Gas collection (e.g. marble chips + HCl → CO₂) — measure volume collected over time
- Mass loss — measure decrease in mass as gas escapes
- Turbidity — reaction produces a precipitate, light transmission decreases
Graphs: Initial gradient = initial rate. Flat line = reaction complete.
Key Points to Remember
- 1Reactions need successful collisions with enough activation energy
- 2Higher temperature: faster particles, more frequent/energetic collisions
- 3Catalyst: lower activation energy, not consumed
- 4Measure rate by gas volume, mass loss, or turbidity
Pakistan Example
Roti Rising — Yeast as a Biological Catalyst
When a daal chawal cook uses yeast to leaven bread, the yeast enzymes (biological catalysts) break down glucose to produce CO₂ gas. The dough rises faster in a warm kitchen — higher temperature increases yeast activity. In industrial bread production in Karachi, temperature is precisely controlled. Grinding spices finer (more surface area) for Pakistani curries is another real-world application of surface area increasing reaction rate.
Quick Revision Infographic
Chemistry — Quick Revision
Rates of Reaction
Key Concepts
Formulas to Know
more frequent/energetic collisionsRoti Rising — Yeast as a Biological Catalyst
When a daal chawal cook uses yeast to leaven bread, the yeast enzymes (biological catalysts) break down glucose to produce CO₂ gas. The dough rises faster in a warm kitchen — higher temperature increases yeast activity. In industrial bread production in Karachi, temperature is precisely controlled. Grinding spices finer (more surface area) for Pakistani curries is another real-world application of surface area increasing reaction rate.