Page 201 - Instant notes
P. 201
Rate laws in action 187
Therefore:
which gives an overall observed rate of reaction of:
Although this rate law is not first order, if the concentration of A is sufficiently high that
the rate of deactivation collisions between A* and A is greater than the rate of
unimolecular reaction of A*, then (i.e. ) and the
rate law simplifies to:
This expression is now a first order rate law in which the observed first order rate
constant, k uni, is a composite of rate constants for underlying elementary reactions:
The Lindemann mechanism is easily adapted to the situation in which activation of A is
dominated by collisions with molecules of a non-reactive diluent bath gas, M, rather than
other molecules of A. The same kinetic approach for the elementary reactions:
gives a rate of product formation:
At any given pressure the concentration of M is constant so the above rate law is
equivalent to a first order rate law: