IP Chemistry Upper Sec 10: Rate of Reactions

These notes align with SEAB GCE O-Level Chemistry (6092) content used in IP programmes (exams from 2026).

Status: SEAB O-Level Chemistry 6092 syllabus (exams from 2026) checked 2025-11-30 - scope unchanged; remains the reference for this note.

What you must know

• Factors: concentration/pressure, temperature, surface area, catalysts (including enzymes).
• Collision theory: rate depends on collision frequency and the fraction of particles with energy ≥ activation energy.
• Catalysts give an alternative pathway with lower activation energy; they are regenerated. Examples: Fe in Haber, V₂O₅ in contact process, enzymes in biology.
• Rate experiments: measure gas volume with gas syringe, mass loss on balance, time for cross to disappear in thiosulfate–acid; plot volume/mass vs time or 1/time proxy.

Detailed notes

• Collision theory: effective collisions need sufficient energy and correct orientation. Higher temperature shifts the Maxwell-Boltzmann curve; more particles exceed Ea, so rate rises sharply. Higher concentration/pressure/surface area increases collision frequency.
• Measurement choices: gas syringe for gases; mass loss on balance for gas escape; “disappearing cross” for turbidity; colour change/clock reactions for solution studies. Control temperature and volumes.
• Typical experiments: $\ce{Mg + HCl}$ (gas volume), marble chips + acid (mass loss or syringe), thiosulfate + acid (time for cross), $\ce{H2O2}$