Factors Affecting Rate, Knowledge Organiser

Five Rate Factors (CCTSP)

• Concentration ↑ → more collisions
• Catalyst → lower Ea, more succeed
• Temperature ↑ → faster + more exceed Ea
• Surface area ↑ → more exposed particles
• Pressure ↑ → same as concentration (gases)

Catalyst Key Facts

• Not consumed — can be reused
• Lowers activation energy
• Provides alternative pathway
• Enzymes = biological catalysts
• Does NOT change amount of product

Graph Interpretation

• Steeper gradient = faster rate
• Same final height = same moles reactant
• Higher plateau = more reactant used
• Horizontal = reaction complete

Exam Checklist

• Temperature: 2 effects needed
• Catalyst: "lowers Ea" not "gives energy"
• End with "more successful collisions"
• Graph: compare steepness AND final value

Key Equations

• Rate = amount ÷ time (g/s or cm³/s)
• Rate increases when: concentration ↑, temperature ↑, surface area ↑, catalyst added, pressure ↑ (gases)
• Catalyst: lowers activation energy — same overall ΔH and same yield

Memory Aid

• C — Concentration (more particles per volume)
• C — Catalyst (lowers activation energy)
• T — Temperature (faster particles, more exceed Ea)
• S — Surface area (more exposed particles)
• P — Pressure (for gases — same as concentration)

Common Mistakes

Misconception 1: "A catalyst is used up in the reaction" A catalyst is not consumed. It provides an alternative pathway with lower activation energy and is reformed at the end of the reaction. This is why the same catalyst can speed up millions of reactions — it is not destroyed. Industrial catalysts (like iron in the Haber process) need replacing eventually due to physical wear, not chemical consumption. Misconception 2: "Increasing temperature gives particles more energy, so more collide" This is partially right but incomplete. Temperature affects rate in two ways: (1) more kinetic energy so more collisions, and (2) crucially, more particles now have energy above the activation energy. Exam questions award marks for both points. Simply saying "particles move faster" only earns partial credit. Misconception 3: "Surface area changes the amount of product formed" Increasing surface area only affects rate — how fast the reaction proceeds. The total amount of product formed depends on the moles of reactants, not their surface area. A powdered marble chip reacts faster with acid than a large lump, but both produce the same total amount of CO₂ if the same mass is used.