A solution and solid state study of niobium complexes University of ...

Chapter 3
A = ∑ ε
cl (3.14)
In chemical kinetics, the rate constant and reaction mechanism can be influenced by
a variety of factors such as temperature, pressure, concentration, homogeneity and
sensitivity to air or light. If the system is kept at constant temperature, constant
pressure and constant volume, the rate constant are now simply the rate of change
in time of any of the reactants or products.
3.6.1 Reaction rate and rate laws
In a closed system, the rate of a chemical reaction can be defined as the change in
concentration of a reactant or product per unit of time. The rate is defined as a
positive quantity that is unaffected by the component whose concentration change is
being measured. For a generalized chemical reaction:
aA + bB cC + dD (3.15)
The rate can be described as a derivative because the rate changes continually with
time. Where t = time and the brackets indicate the concentration of the species:
Rate =
=
52
=
=
(3.16)
The negative signs indicate the disappearance of the compounds. In general, the
rate of reaction can be a function of the concentration of all the species present in a
reaction mixture. Where k is the rate constant and the exponents x and y represent
the order of the reaction with regards to the concentration of A and B:
Rate = k[A] x [B] y (3.17)
The rate constant (k) is independent of the concentrations A and B, but is influenced
by environmental factors such as solvent and temperature changes.
The order of the reaction is determined from the kinetic study and the sum of the
exponents (Eq 3.17) gives the total order of the reaction. Experimentally, great
difficulty is experienced in the determination of these values and in order to
overcome this problem, pseudo-first order conditions are used. Under these