PChem Teaching Lab | Halogenation 1p7

Composite Reactions & the Steady State Approximation

BASIC PRINCIPLES

Review

For a First Order Reaction :

Therefore, a plot of ln([A]_t) versus Time will be linear with Slope = -k and Intercept = ln([A]₀).

Summary

An Elementary Reaction is one which takes place in a single step on the molecular level.

For the general case:

Note : a = a and b = β only if the reaction is elementary.

Order Example Rate Equation Integrated Rate Equation Units of k

0 - d[A]/dt = -k [A]₀ - [A]_t = kt mol dm^-3 s^-1

1 A → B d[A]/dt = -k[A] ln([A]₀/[A]_t) = kt s^-1

2 2A →B d[A]/dt = -2k[A]² (2[A]_t)^-1 - (2[A]₀)^-1 = kt dm³ mol^-1 s^-1

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Chapter 3 - Decomposition of Azomethane

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Order	Example	Rate Equation	Integrated Rate Equation	Units of k
0	-	d[A]/dt = -k	[A]₀ - [A]_t = kt	mol dm^-3 s^-1
1	A → B	d[A]/dt = -k[A]	ln([A]₀/[A]_t) = kt	s^-1
2	2A →B	d[A]/dt = -2k[A]²	(2[A]_t)^-1 - (2[A]₀)^-1 = kt	dm³ mol^-1 s^-1