College Chemistry : Equilibrium

Example Questions

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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 #1 : Equilibrium

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

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 #1 : 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, the reaction will move towards the products.

Yes

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 #31 : Reactions

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 #41 : Reactions

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

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 : Chemical Equilibrium, Equilibrium Constant, And Reaction Quotient

Determine the acid dissociation constant expression for the given reaction.

Explanation:

Acid dissociation constant which is denoted as  is the equilibrium constant for the ionization of an acid. Therefore, the numerator contains the product of the concentrations of the substances on the product side of the chemical equation. The denominator contains the product of the concentrations of the substances on the reactant side of the chemical equation.  is omitted in the acid dissociation constant expression because as the solvent it is in excess and therefore the change in its concentration is negligible in comparison to the other substances in solution.

Example Question #1 : Le Chatelier's Principle

Consider the following equation at equilibrium:

What would happen if more  were added to the system?

There is not enough information to determine the effects of adding more  into the system.

There would be no change in the system.

The reaction would shift towards the products.

The reaction would shift towards the reactants.

The reaction would shift towards the reactants.

Explanation:

Recall Le Chatelier's principle: A chemical system at equilibrium will shift in the direction that minimizes the disturbance to the system.

Before the addition of , the system is in equilibrium, meaning the reaction quotient is equal to the equilibrium constant; .

However, after the addition of , a product, the reaction quotient is now less than the equilibrium constant; .

In order to maintain equilibrium, the reaction will then shift left to favor the reactants in this chemical system.

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