Chapter 17.1, Problem 8SSC

Interpretation Introduction

Interpretation:

The relation of size of equilibrium constant with amount of products is to be discussed.

Concept introduction:

The equilibrium constant expresses the relationship between product and reactants of a reaction at equilibrium.

The equilibrium constant is denoted by ${\text{'K}}_{\text{C}}\text{'}$.

$a)A+B\rightleftharpoons C+D$.

$\text{Reactants}\rightleftharpoons \text{Products}$

${\mathrm{K}}_C$ for this reaction

${\mathrm{K}}_C=\frac{[C][D]}{[A][B]}$

$b)aA+bB\rightleftharpoons cC+dD$.

${\mathrm{K}}_C=\frac{{[C]}^c{[D]}^d}{{[A]}^a{[B]}^b}$

In this reaction $[A][B][C][D]$ are the equilibrium concentration of the reactant and product. Therefore, ${\mathrm{K}}_C=\frac{[Product]}{[Reactant]}$

Answer to Problem 8SSC

If $K_C>1$, amount of product formed is more than reactant.

If $K_C<1$, amount of product formed is less than reactant.

Explanation of Solution

For the reaction:

$A+B\rightleftharpoons C+D$.

$\text{Reactants}\rightleftharpoons \text{Products}$

${\mathrm{K}}_C$ for this reaction is given by:

${\mathrm{K}}_C=\frac{[C][D]}{[A][B]}$

Thus $K_C>1$, product of concentration of products is more than reactants.

$K_C<1$, product of concentration of products is less than reactants.

if $K_C$ is very large in size, the reaction proceeds near to completion.

$H_2(g)+C{l}_2(g)\rightleftharpoons 2HCl(g)$

At 300K has

$K_C=4.0\times {10}^{31}$

On the other hand,

If $K_C<1$ reactant predominates.

Conclusion

Thus size of equilibrium constant is related to amount of products.