PChem Teaching Lab | Halogenation 1p3c

Composite Reactions & the Steady State Approximation

BASIC PRINCIPLES

Hint

For the general case :

Note the signs : -ve before a reactant and +ve before a product.

Example :

For the reaction 2A → B, the rate of reaction can be expressed as:
r = - ½ d[A]/dt = + d[B]/dt

Note : The d[A]/dt term is prefixed with -(1/2) since there are two A molecules as reactants, and the d[B]/dt term is prefixed with +(1/1) since there is one B molecule as a product.

Review Question

For the reaction NO + NO₃ → 2NO₂ , the rate of reaction can be expressed as

r = + d[NO]/dt = + d[NO₃]/dt = - ½ d[NO₂]/dt
r = + d[NO]/dt = + d[NO₃]/dt = - d[NO₂]/dt
r = - d[NO]/dt = + d[NO₃]/dt = + ½ d[NO₂]/dt
r = - d[NO]/dt = - d[NO₃]/dt = + ½ d[NO₂]/dt
r = - d[NO]/dt = - d[NO₃]/dt = + d[NO₂]/dt