📘 IB Understanding
Sketch, identify and analyse graphical representations of zero, first and second order reactions from rate-concentration graphs.
Rate-concentration graphs reveal the order of reaction with respect to a specific reactant by showing how the rate responds to changes in concentration.
Interpreting Rate-Concentration Graphs
The visual shape of a rate vs [A] graph is directly linked to the mathematical exponent (order) in the rate equation. Analysing these graphs allows us to identify the order of reaction with respect to a specific reactant.
| Order | Rate Equation | Graph Shape | Mathematical Meaning |
|---|---|---|---|
| Zero Order | Rate = k[A]⁰ = k | Horizontal straight line | Rate is independent of concentration. Changing [A] does not affect the rate, resulting in a constant value. |
| First Order | Rate = k[A]¹ | Straight line through origin | Rate is directly proportional to concentration. If [A] doubles, the rate doubles. The gradient represents the rate constant, k. |
| Second Order | Rate = k[A]² | Upward parabolic curve | Rate is proportional to the square of the concentration. If [A] doubles, the rate increases by a factor of four (2² = 4). |
⚠️ Common Mistake
Students often confuse the zero-order concentration-time graph (a straight diagonal line going down) with the first-order rate-concentration graph (a straight diagonal line going up). Always check the axis labels before interpreting a graph!
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