Topic 6.2.4 · Core
Interpreting Rate Graphs
The story of a reaction — told through a curve.
The Big Picture: Every rate graph is a reaction's biography. The steepness (gradient) tells you the rate. The final plateau height tells you how much product formed — which depends only on the limiting reactant's amount, never on temperature or catalyst.
The Three Golden Rules
📐
Gradient = Rate
Steeper slope → faster reaction. Flattest at the end (zero rate).
🏔️
Start = Max Rate
Highest concentration at T=0, so steepest gradient is always at the beginning.
📦
Plateau = Moles
Final volume depends only on AMOUNT of limiting reactant — not speed of reaction.
🔬 The Visual Laboratory — Toggle Curves
Switch curves on/off. Notice: Red and Blue plateau at the SAME height. Green doubles it.
💡 Click on a curve to analyse that point.
⚠️ The Examiner's Top 4 Traps
❌ Student says: ""Higher temperature makes more gas.""
✅ Examiner wants: FALSE — temperature speeds up the reaction but cannot change the amount of product (that depends on moles).
❌ Student says: ""The reaction stops when gas runs out.""
✅ Examiner wants: FALSE — the reaction stops when the LIMITING REACTANT is used up.
❌ Student says: ""A catalyst changes the final volume.""
✅ Examiner wants: FALSE — a catalyst only increases rate, not yield.
❌ Student says: ""The initial rate is the steepest anywhere.""
✅ Examiner wants: CORRECT but only at T=0 — concentration is highest at the very start, so gradient is steepest there.
Topic 6.2.4 Core · Cambridge IGCSE Chemistry 0620 · 2026–2028 Syllabus
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