The
differential rate law (equation) has the general form: rate = k[A]
x[B]
y.
The
magnitudes of exponents x and y are important
clues as to the
pathway for the reaction.
One way of determining
- the exponent x of [A] is to measure the rate at the beginning of the reaction (before product buildup affects the rate) for different initial concentrations of A.
If doubling [A] while holding [B] constantdoes not change reaction rate, then x = 0
doubles reaction rate, then x = 1
quadruples reaction rate, x = 2
- the exponent y of [B] is to vary the initial concentration of B while keeping [A] constant and apply the above.
- the magnitude of the rate constant k once x and y are known, is to substitute an experimental rate and the concentration(s) of A and B at that rate into the rate law.
The magnitude of k is equal to the rate of the reaction when the concentration of each substance in the rate law is 1 mol L–1.
The unit of k depends on the order of the reaction and is (L mol–1)n–1 s–1 where n equals x + y.