Determination of Reaction Order

• Determination of Reaction Order defines how reactant concentration influences reaction rate.
• Determining the order of a degradation reaction involves monitoring concentration over time and fitting data to various integrated rate equations.

Methods of Determination of Reaction Order:

1. Graphical Method

   • Plot concentration vs. time for different rate laws:
     • Zero order: [A] vs. time (linear)
     • First order: time (linear)
     • Second order: time (linear)
   • The one that gives a straight line indicates the reaction order.

2. Method of Initial Rates

   • Run multiple experiments with different initial concentrations.
   • Measure the initial rate.
   • Use:
   • $\text{Rate} = k[A]^n \;\;\Rightarrow\;\; \log(\text{Rate}) = \log(k) + n \log([A])$
   • $\text{Plot } \log(\text{Rate}) \; \text{ vs. } \log([A]) \rightarrow \text{Slope} = n$

3. Half-Life Method

   • Measure how half-life changes with initial concentration:
     • Zero-order: t_{1/2} \propto [A]_0
     • First-order: t_{1/2} = \text{constant}
     • Second-order: t_{1/2} \propto \frac{1}{[A]_0}

4. Curve Fitting Software

   • Use software (e.g., WinNonlin, Excel, MATLAB) to fit experimental data to kinetic models

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