# Boyleâ€™s Law

Chemical equilibrium is achieved when the rate of the forward and reverse reactions is equal and the concentrations of the reactants and products remain constant. Chemical equilibria are stable and dynamic in nature.

If the reactants and products in a system are in the same phase, the equilibrium is said to be homogeneous.

A phase is a homogeneous (same composition and properties throughout) part of a system, separated from other phases (or homogeneous parts) by bounding surfaces.

If more than one phase is present in a chemical equilibrium, it is said to be heterogeneous equilibrium.

- Let us consider the following equilibrium reaction
*K*_{eq}) will be*d*/*M*(where*d*and*M*represent the density and molar mass, respectively). This ratio of*d*/*M*will be a constant whether X is present initially or at equilibrium. This means that the concentration of X is not varying, but is a constant, which can be merged with*K*_{eq}to give another constant called*K*._{c}*K*involves only those species whose concentration changes during the reaction._{c}*K*_{eq}and*K*is that the expression of_{c}*K*_{eq}involves all species (whether they are pure solids, pure liquids, gases, solvents, or solutions), while the expression*K*involves only those species whose concentration is a variable (such as gases and solutions). Thus, expression_{c}*K*is devoid of pure components (such as pure solids and pure liquids) and solvents._{c}*P*_{Z}/*P*_{Y}would also be a constant, represented by K_{P}. Therefore, - Now, let us change the phase of reactant X from pure solid to solution and add another gaseous product. The equilibrium reaction can now be represented as:
*a*, which is dissolved in*V*liter of solvent. So, the initial concentration of X is*a*/*V*. Now at equilibrium, the moles of X reacted with Y is*x*. Thus, the concentration of X now becomes (*a*âˆ’*x*)/*V*. This shows that the concentration of X changes during the reaction and X is thus a variable. Thus, the given expression of*K*_{eq}involves all variable terms, so the ratio can also be referred as*K*. Therefore,_{c}*K*,_{c}*R*, and*T*all are constant), which implies that the RHS will also be a constant. But RHS of the expression can neither be called*K*(as all are not partial pressure terms) nor_{P}*K*(as all are not concentration terms). So such expression that involves both partial pressure and concentration terms are referred as_{c}*K*_{PC}. Therefore,*K*can exist only for that equilibrium which satisfies the following two conditions:_{P}- At least one of the reactant or product should be in gaseous phase.
- No component of the equilibrium should be in the solution phase (because when solution is present, the equilibrium constant would be called
*K*_{PC}).

- For the equilibrium of type:
*n*_{1}A_{(g)}+*n*_{2}B_{(g)}*m*_{1}C_{(g)}+*m*_{2}D_{(g)},*K*=_{P}*K*(_{c}*RT*)^{Î”n}*n*= Sum of stoichiometric coefficient of the gaseous product(s)