Everything about Chemical Equilibrium totally explained
In a
chemical process,
chemical equilibrium is the state in which the
chemical activities or
concentrations of the reactants and products have no net change over time. Usually, this would be the state that results when the forward
chemical process proceeds at the same rate as their
reverse reaction. The
reaction rates of the forward and reverse reactions are generally not zero but, being equal, there are no net changes in any of the reactant or product concentrations. This process is called
dynamic equilibrium
Introduction
In a
chemical reaction, when reactants are mixed together in a reaction vessel (and heated if needed), the whole of reactants don't get converted into the products. After some time (which may be shorter than millionths of a second or longer than the age of the universe), there will come a point when a fixed amount of reactants will exist in harmony with a fixed amount of products, the amounts of neither changing anymore. This is called chemical equilibrium.
The concept of chemical equilibrium was developed after
Berthollet (1803) found that some
chemical reactions are
reversible. For any reaction such as
»
to be at equilibrium the
rates of the forward and backward (reverse) reactions have to be equal. In this
chemical equation with harpoon arrows pointing both ways to indicate equilibrium, A and B are
reactant chemical species, S and T are product species, and
α,
β,
σ, and
τ are the
stoichiometric coefficients of the respective reactants and products. The equilibrium position of a reaction is said to lie far to the right if, at equilibrium, nearly all the reactants are used up and far to the left if hardly any product is formed from the reactants.
Guldberg and
Waage (1865), building on Berthollet’s ideas, proposed the
law of mass action:
»
(For proof see
Lagrange multipliers)
This is a set of
(m+k) equations in
(m+k) unknowns (the
and the
) and may, therefore, be solved for the equilibrium concentrations
as long as the chemical potentials are known as functions of the concentrations at the given temperature and pressure. (See
Thermodynamic databases for pure substances).
This method of calculating equilibrium chemical concentrations is useful for systems with a large number of different molecules. The use of
k atomic element conservation equations for the mass constraint is straightforward, and replaces the use of the stoichiometric coefficient equations.
[Further Information]
Get more info on 'Chemical Equilibrium'.
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