03Class 12 Chemistry

Chemical Kinetics formulas

Rate law, integrated rate equation and Arrhenius formulas for Chemical Kinetics. Check the units of k, since they reveal the order of the reaction.

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All Chemistry formulas

Rate

Rate law: $\displaystyle \text{rate} = k[A]^x[B]^y$
Order x + y comes from experiment, not the balanced equation.
Units of k: $\displaystyle (\text{mol L}^{-1})^{1 - n}\,\text{s}^{-1}$
n is the order.

Integrated rate equations

Zero order: $\displaystyle [R] = [R]_0 - kt, \quad t_{1/2} = \frac{[R]_0}{2k}$
First order: $\displaystyle k = \frac{2.303}{t}\log\frac{[R]_0}{[R]}$
First order half-life: $\displaystyle t_{1/2} = \frac{0.693}{k}$
Doesn't depend on initial concentration.

Temperature

Arrhenius equation: $\displaystyle k = Ae^{-E_a/RT}$
Two temperatures: $\displaystyle \log\frac{k_2}{k_1} = \frac{E_a}{2.303R}\left(\frac{T_2 - T_1}{T_1T_2}\right)$

Where students slip up

Taking the order from the balanced equation. It's found by experiment.
Confusing order and molecularity. Molecularity is always a whole number and applies to one elementary step.
Thinking a catalyst changes ΔG or K. It lowers Eₐ only.

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