Equilibrium and the direction of reaction

The isomerisation of glucose in aqueous solution can be used to illustrate this. 

The concentrations of the a and (3 forms found at various times throughout reaction are given in Table 2.1. 

The difference between a quotient or product of concentrations for situations not at equilibrium, and that for equihbrium can be further illustrated by considering the following equilibrium  

In this case when equilibrium is established all three species are present. The equilibrium product is ([Sr +JpO ]) and this takes a constant value at any given temperature. If solutions of Sr(N03 2(aq) and K2S04(aq) are mixed, predictions can be made as to whether equilibrium between SrS04(s), Sr (aq) and S04 (aq) can be set up for given compositions of the mixture. 

If initially the quotient, [Sr +JpO ] ([Sr lfSO ]), then reaction would occur so that the product can decrease to the equilibrium value, i.e. the back reaction would occur and precipitation of SrS04 would occur. This would continue until the concentrations had decreased sufficiently so that [Sr +][S04 ] = ([Sr +][S04 ])gq, at which stage equilibrium is established. 

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