Reaction Kinetics:

1. Introduction
Chemical reaction kinetics deals with the rates of chemical processes. Any chemical process may be broken down into a sequence of one or more single-step processes known either as elementary processes, elementary reactions, or elementary steps. Elementary reactions usually involve either a single reactive collision between two molecules, which we refer to as a a bimolecular step, or dissociation/isomerisation of a single reactant molecule, which we refer to as a unimolecular step. Very rarely, under conditions of extremely high pressure, a termolecular step may occur, which involves simultaneous collision of three reactant molecules. An important point to recognise is that many reactions that are written as a single reaction equation in actual fact consist of a series of elementary steps. This will become extremely important as we learn more about the theory of chemical reaction rates.
2. Rate of reaction:-
When we talk about the rate of a chemical reaction, what we mean is the rate at which reactants are used up, or equivalently the rate at which products are formed. The rate therefore has units of concentration per unit time, mol dm-3 s-1 (for gas phase reactions, alternative units of concentration are often used, usually units of pressure – Torr, mbar or Pa). To measure a reaction rate, we simply need to monitor the concentration of one of the reactants or products as a function of time. There is one slight complication to our definition of the reaction rate so far, which is to do with the stochiometry of the reaction. The stoichiometry simply refers to the number of moles of each reactant and product appearing in the reaction equation. For example, the reaction equation for the well-known Haber process, used industrially to produce ammonia, is:
1. Introduction
Chemical reaction kinetics deals with the rates of chemical processes. Any chemical process may be broken down into a sequence of one or more single-step processes known either as elementary processes, elementary reactions, or elementary steps. Elementary reactions usually involve either a single reactive collision between two molecules, which we refer to as a a bimolecular step, or dissociation/isomerisation of a single reactant molecule, which we refer to as a unimolecular step. Very rarely, under conditions of extremely high pressure, a termolecular step may occur, which involves simultaneous collision of three reactant molecules. An important point to recognise is that many reactions that are written as a single reaction equation in actual fact consist of a series of elementary steps. This will become extremely important as we learn more about the theory of chemical reaction rates.
2. Rate of reaction:-
When we talk about the rate of a chemical reaction, what we mean is the rate at which reactants are used up, or equivalently the rate at which products are formed. The rate therefore has units of concentration per unit time, mol dm-3 s-1 (for gas phase reactions, alternative units of concentration are often used, usually units of pressure – Torr, mbar or Pa). To measure a reaction rate, we simply need to monitor the concentration of one of the reactants or products as a function of time. There is one slight complication to our definition of the reaction rate so far, which is to do with the stochiometry of the reaction. The stoichiometry simply refers to the number of moles of each reactant and product appearing in the reaction equation. For example, the reaction equation for the well-known Haber process, used industrially to produce ammonia, is: