CHM050 · Kinetics & Catalysis · Classes 11–12
Concentration vs Rate Graph
Objective: To interpret a concentration–time graph and find the rate from its slope.
🧰 Virtual materials and apparatus
- Virtual concentration–time graph
- Tangent line
📐 Formulas and SI units
rate = −Δ[A]/Δt
first order: [A] = [A]₀e^(−kt), rate = k[A]
💡 Theory
Reaction rate is the change in concentration per unit time. On a concentration–time curve the rate at any instant is the slope of the tangent. For a first-order reaction C = C₀e^(−kt) and the rate = kC, so the rate falls as the reactant is used up.
🪜 Guided virtual procedure
- Set C₀ = 1 mol/L and k = 0.1 /s.
- Move t and watch the tangent.
- Read the instantaneous rate and the average rate.
- Change k and compare the curves.
- Explain why the curve flattens.
📋 Observations Simulated values
✅ Result and conclusion
After 10 s the concentration is 0.368 mol/L and the rate is 0.0368 mol/(L s); the average rate over 10 s is 0.0632 mol/(L s).
🔬 Real lab vs simulation
Real data are measured by colorimetry, gas volume or titration and scatter around the ideal curve. Data here are simulated.
⚠️ Safety
Simulated dataset only. Real laboratory chemicals are handled only by teachers.
❓ Quick check
1. The rate at a moment is the…
2. As a reaction proceeds, rate usually…
3. Unit of rate?
🏋️ Practice
Easy[A] after 20 s (default)?
Answer: ≈ 0.135 mol/L
MediumRate at t = 0 (default)?
Answer: 0.1 mol/(L s)
ChallengeHalf-life for k = 0.1 /s?
Answer: 6.93 s