The complete lecture — reaction rates come alive in the live panel as you read. Scroll down; the animation keeps pace, and you can drive the rate simulator yourself.
1 — Rate of a reaction
Raterate = −Δ[reactant]/Δt = +Δ[product]/Δt · unit mol dm⁻³ s⁻¹
2 — Factors affecting the rate
Concentration, temperature, surface area, pressure and a catalyst all change the rate. Drag the sliders in the live panel: more particles or faster particles → more collisions → faster rate.
3 — Rate law & rate constant
aA + bB → productsrate = k [A]ᵐ [B]ⁿ
4 — Order of reaction
| Order | Rate |
|---|
| zero | rate = k |
| first | rate = k[A] |
| second | rate = k[A]² |
5 — Molecularity vs order
The slowest step is the rate-determining step.
6 — Collision theory
- Particles must collide.
- An effective collision needs energy ≥ Ea and correct orientation.
7 — Activation energy & the energy profile
- Activation energy (Ea) — minimum energy to react. The peak is the activated complex.
8 — Effect of temperature
Arrheniusk = A e^(−Ea/RT) · ~10 °C rise ≈ doubles the rate
9 — Effect of a catalyst
- Catalyst — lowers Ea via an alternative path; not consumed; doesn't change K.
10 — Measuring the rate
- Gas volume / mass loss / colorimetry / conductivity / precipitate timing.
11 — Worked numericals
order
[A] doubles → rate doubles ⇒ first order
k
k = rate/[A] = 4×10⁻³ / 0.2 = 0.02 s⁻¹
12 — Exam recap
- Rate definition & units.
- Factors affecting rate.
- Rate law, order & rate constant.
- Molecularity; rate-determining step.
- Collision theory & activation energy.
- Temperature (Arrhenius) & catalysis.