What Does the Equilibrium Constant Tell Us

We have seen that the equilibrium constant for a given reaction can be calculated from known equilibrium concentrations. Once we know the value of the equilibrium constant, we can use Equation (14.2) to calculate unknown equilibrium concentrations— remembering, of course, that the equilibrium constant has a constant value only if the temperature does not change. In general, the equilibrium constant helps us to predict the direction in which a reaction mixture will proceed to achieve equilibrium and to calculate the concentrations of reactants and products once equilibrium has been reached. These uses of the equilibrium constant will be explored in this section. 

The equilibrium constant for the formation of hydrogen iodide from molecular hydrogen and molecular iodine in the gas phase 

Keep in mind that the method for calculating Q is the same as that for K, except that nonequilibrium concentrations are used. 

For reactions that have not reached equilibrium, such as the formation of HI considered above, we obtain the reaction quotient (QJ, instead of the equihbrium constant by substituting the initial concentrations into the equilibrium constant expression. To determine the direction in which the net reaction will proceed to achieve equilibrium, we compare the values of 2c and K. The three possible cases are as follows  

Qc The ratio of initial concentrations of products to reactants is too small. To reach equilibrium, reactants must be converted to products. The system proceeds from left to right (consuming reactants, forming products) to reach equilibrium. 

The quantity obtained by substituting the initial concentrations into the equilibrium constant expression is called the reaction quotient (QJ. To determine in which 

The direction of a reversible reaction to reach equilibrium depends on the relative magnitudes of and 

Reactants — Products Equilibrium no net change Reactants — Products 

Strategy We are given the initial amounts of the gases (in moles) in a vessel of known volume (in liters), so we can calculate their molar concentrations and hence the reaction quotient (Qc). How does a comparison of with enable us to determine if the system is at equilibrium or, if not, in which the direction the net reaction will 

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Equilibrium constants range over many orders of magnitude. Values as small as 10 are known, as are values as high as 10 or greater. What does the size of the equilibrium constant tell us about the reaction If we look at the equilibrium expression for a reaction as an algebraic relationship, the answer will become apparent. 

What is the significance of the equilibrium constant What does a large equilibrium constant tell us about a reaction A small one ... 

What does the value of an equiUbrium constant tell us about the time required for the reaction to reach equilibrium ... 

Given this definition of an equilibrium constant, what does it tell us For example, what does a large equilibrium constant (Kgq 1) imply about a reaction It means that the forward reaction is largely favored and that there will be more products than reactants when equilibritun is reached. For example, consider the reaction ... 

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