Welcome back again.Last session we seen reactions and rate laws.Now this session we try to know how rate constant applied to reaction depends on rate laws.
The half life, t1/2, of a substance is defined as the time it takes for the concentration of the substance to fall to half of its initial value...
A kinetics experiment consists of measuring the concentrations of one or more reactants or products at a number of different times during the reaction
In kinetics, a ‘complex reaction’ simply means a reaction whose mechanism comprises more than one elementary step. In the previous sections we have looked at experimental methods for measuring reaction rates to provide kinetic data that may be compared with the predictions of theory. In the following sections, we will look at a range of different types of complex reactions and the rate laws that may be predicted from their kinetic mechanisms. Disagreement of a predicted rate law with the experimental data is enough to rule out the corresponding proposed mechanism, while agreement inspires some confidence that the proposed mechanism is the correct one. It should be noted though that agreement between the predicted and measured kinetics is not always enough to assign a mechanism. The proposed mechanism must be able to account for all other properties of the reaction, which may include quantities such as the product distribution, product stereo chemistry, kinetic isotope effects, temperature dependence, and so on.
The types of complex mechanisms that we will cover are: consecutive (or sequential) reactions;competing reactions; pre-equilibria; uni molecular reactions; third order reactions; enzyme reactions;chain reactions; and explosions.
If the rate constants for the following reaction are k1 and k2 .
General Example ;
A & B are the two reactants which gives a product C after the reaction.
For reactant A
.... continued
5. Integrated rate laws
A rate law is a differential equation that describes the rate of change of a reactant (or product) concentration with time. If we integrate the rate law then we obtain an expression for the concentration as a function of time, which is generally the type of data obtained in an experiment.In many simple cases, the rate law may be integrated analytically....
6.Half lives
The half life, t1/2, of a substance is defined as the time it takes for the concentration of the substance to fall to half of its initial value...
7.Determining the rate law from experimental data
A kinetics experiment consists of measuring the concentrations of one or more reactants or products at a number of different times during the reaction
8.Complex reactions
In kinetics, a ‘complex reaction’ simply means a reaction whose mechanism comprises more than one elementary step. In the previous sections we have looked at experimental methods for measuring reaction rates to provide kinetic data that may be compared with the predictions of theory. In the following sections, we will look at a range of different types of complex reactions and the rate laws that may be predicted from their kinetic mechanisms. Disagreement of a predicted rate law with the experimental data is enough to rule out the corresponding proposed mechanism, while agreement inspires some confidence that the proposed mechanism is the correct one. It should be noted though that agreement between the predicted and measured kinetics is not always enough to assign a mechanism. The proposed mechanism must be able to account for all other properties of the reaction, which may include quantities such as the product distribution, product stereo chemistry, kinetic isotope effects, temperature dependence, and so on.
The types of complex mechanisms that we will cover are: consecutive (or sequential) reactions;competing reactions; pre-equilibria; uni molecular reactions; third order reactions; enzyme reactions;chain reactions; and explosions.
9.Consecutive reactions
If the rate constants for the following reaction are k1 and k2 .
General Example ;
A + B → C
A & B are the two reactants which gives a product C after the reaction.
The the rate equation can be written as ;
For reactant A
d[A] / dt = - k1 [A]
For Reactant B :
For Reactant B :
d[ B ] / dt = k1 [A] - K2 [B]
and for product C
d[C] / dt - k2[ B ]
.... continued
