RATE OF REACTIONS

Rate of reactions

The rate of reaction tells us how fast a number of moles of one chemical species are being consumed to form another chemical species.

• The term chemical species refers to any chemical component or element with a given identity.
• The identity of a chemical species is determined by the kind, number, and configuration of that species atoms.

Chemical reaction has taken place when a detectable number of molecules of one or more species have lost their identity and assumed a new form by a change in the kind or number of atoms in the compound and/or by a change in structure or configuration of these atoms.

• In this classical approach to chemical change, it is assumed that the total mass is neither created nor destroyed when a chemical reaction occurs.
• The mass referred to is the total collective mass of all the different species in the system.
• However when considering the individual species involved in a particular reaction, we do speak of the rate of disappearance of mass of a particular species.
• The rate of disappearance of a species say species A is the number of A molecules that lose their chemical identity per unit time per unit volume through the breaking and subsequent re-forming of chemical bonds during the course of the reaction.
• In order for a particular species to "appear" in the system some prescribed fraction of another species must lose its chemical identity.
• There are three basic ways a species may lose its chemical identity:

1. Decomposition:- ln decomposition the molecule loses its identity by being broken down into smaller molecules. atoms. or atom fragments. 
2. Combination:- A molecule may lose its species identity is through combination with another molecule or atom.
3. Isomerization:- Here, although the molecule neither adds other molecules to itself nor breaks into smaller molecules. it still loses its identity through a change in configuration.