When people say that diamonds are forever, they are actually not being factually correct. Diamonds have a tendency to convert into graphite, another allotropic form of carbon. But the speed at which this transformation takes place is so slow that diamonds are bound to stay in the same form forever. The field of chemistry that allows scientists to decide that diamonds are unstable is chemical thermodynamics. And the field of chemistry that allows them to discern that in spite of their unstable nature they will almost never convert into graphite is chemical kinetics.
A reaction rate determines how fast or slow a reaction will go. It is defined as the decrease in concentration of a reactant or the increase in concentration of the product, as reactants undergo a change to form the products. The reaction rate helps scientists in deriving the rate laws for a reaction and the rate constants. These rate laws are mathematical representation of what is actually going on and how it will proceed. Rate laws help in predicting how much time it will take for a certain amount of product to be formed from the reactants.
Any change that takes place when one or more reactants convert into one or more products has to deal with the configuration of atoms. The bonds between the atoms have to be broken up and new bonds have to be formed. Both the states in which the atoms were before the change and after the change have some energies associated with them. Usually, the reactants have a higher energy associated with them and the products have a lower energy. This allows the reactants to readily form products because a lower energy state offers more stability. In between the change, the reactants are in an unstable transition state because the atoms are bound together with partial bonds, old and new. This transition state has a much higher energy associated with it. It is this steep rise in energy that has to be overcome for the reactants to change into products.
What does reaction rate depend on?
The reaction rate depends on a number of factors:
1. Physical state
The physical state of the reactants determine the surface area over which the reaction can take place. If the solid reactants are finely crushed or if the reactants are in an aqueous phase, then the reaction can take place faster because more area is available for interaction between the two.
Reactions are a product of collision between the various reactants involved in the reaction. If the number of participating reactant molecules is increased, the probability of them colliding and resulting into a reaction will also increase.
Increasing the temperature is the most straightforward way to ensure that the reactants are able to overcome the energy gap in order to achieve the transition state since increasing the temperature increases the energy of the reactant molecules.
A catalyst is any substance that increases the reaction rate but it does not undergo a chemical change itself. Usually, the catalysts function by providing an alternative reaction mechanism which has lower energy of transition associated with it.