# College Chemistry : Chemical Equilibrium, Equilibrium Constant, and Reaction Quotient

## Example Questions

### Example Question #1 : Chemical Equilibrium, Equilibrium Constant, And Reaction Quotient

Consider the following reaction:

Give the expression for the equilibrium constant for this reaction.

Explanation:

Recall how to find the expression of the equilibrium constant for the simplified equation:

Since the given equation has gases, we will only consider the partial pressures of each gas in the expression for the equilibrium constant. Remember that only molecules in aqueous and gas forms are included in this expression. Pure solids and pure liquids are excluded.

Thus, we can then write the following equilibrium constant for the given equation:

### Example Question #2 : Chemical Equilibrium, Equilibrium Constant, And Reaction Quotient

Consider the following reaction:

The reaction mixture at  initially contains  and . At equilibrium, . What is the equilibrium constant for the reaction?

Explanation:

Start by writing the equilibrium expression:

Now, create a chart like the following to keep track of the changes in concentration.

 Initial 0.750 2.00 0.00 Change -0.100 -0.025 0.200 Equilibrium 0.650 19.75 0.200

Since we know that the concentration of HCl decreased by , we can use the stoichiometric ratios to deduce the amount of change for the oxygen gas and the chlorine gas.

Plug in the equilibrium concentrations into the expression for the equilibrium constant.

### Example Question #3 : Chemical Equilibrium, Equilibrium Constant, And Reaction Quotient

Calculate the equilibrium constant at  for the reaction by using free energies of formation.

Explanation:

Start by using the free energies of formation to find .

Recall the equation that links together  with the equilibrium constant, .

Plug in the given information and solve for .

### Example Question #4 : Equilibrium

Consider a reaction mixture using the equation shown. At equilibrium the partial pressure of  is  and the partial pressure of  is . What is the partial pressure of  in this mixture if  at ?

or

or

or

or

or

Explanation:

Use algebra to solve for the partial pressure of .

### Example Question #4 : Chemical Equilibrium, Equilibrium Constant, And Reaction Quotient

Considering the reaction shown, if the partial pressures of , and  are  each, is the mixture at equilibrium? If not which direction will the reaction proceed to reach equilibrium if ?

No, reaction will proceed right towards the products.

Yes

Yes, the reaction will move towards the products.

No, the reaction will proceed left towards the reactants.

No, reaction will proceed right towards the products.

Explanation:

Since  the reaction is not at equilibrium. This means that at equilibrium, the ratio of products to reactants is greater than at the given conditions. Thus, the reaction will move right towards the products to reach equilibrium.

### Example Question #6 : Equilibrium

In the laboratory  of  and  of  are reacted in a  beaker. At equilibrium  of  remain. Using the equation shown calculate the equilibrium constant.

Explanation:

Use an ice table and the  equation to solve.

Initial

Change

Equilibrium

### Example Question #7 : Equilibrium

Find the  of the reaction if you start with  and end with  at .

Explanation:

Use an ICE table and the  equation to solve.

Initial

Change

Equilibrium

### Example Question #8 : Equilibrium

Hypobromous acid will dissociate in water at  with a . What is the  for this dissociation process?

Explanation:

For this question, we're given the acid dissociation constant for a reaction that occurs at a given temperature. We're asked to find the standard free energy change for the reaction.

First, we're going to need to use an equation that relates standard free energy changes with an equilibrium constant, which is shown as follows.

With regards to the temperature, we will need to convert the units given in the question stem into units of Kelvin.

Knowing that  is the ideal gas constant, we have all the information we need to solve for the value of .

### Example Question #9 : Equilibrium

Determine the acid dissociation constant expression for the given reaction.