Key facts & rules

• Collision theory: reaction occurs when particles collide with sufficient energy (≥ activation energy) and correct orientation.
• Temperature ↑: more frequent collisions AND more particles have energy ≥ Ea → rate increases.
• Concentration ↑ (or pressure ↑ for gases): more frequent collisions → rate increases.
• Surface area ↑ (smaller particles): more exposed particles → more frequent collisions → rate increases.
• Catalyst: provides alternative reaction pathway with lower activation energy → more particles have enough energy → rate increases (not consumed).
• Measuring rate: volume of gas produced per second, or decrease in mass per second, or colour change.
• A graph of volume vs time: steeper gradient = faster rate; gradient decreases as reactants are used up.