Chemical EquilibriumChemical Equilibrium

Reaction Types Reaction Types

So far this year we have been So far this year we have been writing chemical formulas as writing chemical formulas as completioncompletion reaction. reaction.

In other words, the reaction In other words, the reaction completelycompletely goes to products. goes to products.

We represented this by using We represented this by using in the chemical equation.in the chemical equation.

Example: Example:

SS88 + 8O + 8O22 8SO 8SO22

Reversible ReactionsReversible Reactions

However, many of the reactions we However, many of the reactions we study are actually study are actually reversiblereversible..

ReversibleReversible reactions are chemical reactions are chemical reactions in which the products reactions in which the products re-re-formform the original reactants. the original reactants.

Eventually, a chemical Eventually, a chemical equilibriumequilibrium is is formed or a state of formed or a state of balancebalance where where the the raterate forwardforward reaction equals the reaction equals the raterate in in reversereverse..

Chemical equilibria are Chemical equilibria are dynamicdynamic In other words, even though it In other words, even though it

looks like the reaction has looks like the reaction has stoppedstopped, the substances are still , the substances are still reactingreacting..

However, for every However, for every newnew product product that was made, an that was made, an oldold product product turned back into turned back into reactantreactant..

Note that this does Note that this does notnot mean that mean that products and reactants need to products and reactants need to be equal in be equal in concentrationconcentration. .

That is why we have That is why we have the the EquilibriumEquilibrium ConstantConstant A number that relates the A number that relates the

concentrations of concentrations of startingstarting materials materials to to productsproducts of a of a reversiblereversible reaction reaction at a given temperature.at a given temperature.

Symbolized by Symbolized by KKeqeq

They do They do notnot have units have units Remember, concentrations are Remember, concentrations are

expressed in expressed in molarity (mol/L)molarity (mol/L)

KKeqeq can show whether can show whether a reaction is favorablea reaction is favorable If KIf Keqeq equals a equals a largelarge number, then there number, then there

will be more will be more productsproducts than than reactantsreactants. . (bigger arrow pointing to the (bigger arrow pointing to the rightright))

Reactions that produce more products Reactions that produce more products than reactants are known as than reactants are known as favorablefavorable..

If KIf Keqeq equals a equals a smallsmall number, then there number, then there will be more will be more reactantsreactants than than productsproducts. . (bigger arrow pointing to the (bigger arrow pointing to the leftleft))

If the value is If the value is 11, then it is , then it is 50:5050:50

How do we determine How do we determine if Kif Keqeq is small or large? is small or large?

We need to write the We need to write the KKeqeq formula formula ((expressionexpression) for the reaction) for the reaction

Remember, these constants only Remember, these constants only apply to equations in apply to equations in equilibriumequilibrium

Step 1 – Write the Step 1 – Write the balancedbalanced equationequation for the reaction. for the reaction.

Step 2 – Write the Step 2 – Write the equilibrium equilibrium expression.expression. Place the product concentrations in Place the product concentrations in

the the numeratornumerator and the reactant and the reactant concentration in the concentration in the denominatordenominator..

All will be All will be multipliedmultiplied This is done by writing each ion, This is done by writing each ion,

compound, etc, in compound, etc, in bracketsbrackets Leave out any Leave out any solidssolids or pure or pure liquidsliquids This includes This includes waterwater if dealing with if dealing with

an an aqueousaqueous solution solution

Step 3Step 3

Complete the equilibrium Complete the equilibrium expressionexpression

This is done by This is done by raisingraising each each concentration by its concentration by its coefficientcoefficient from the from the balancedbalanced equation. equation.

ExamplesExamplesCaCOCaCO33(s) + 2H(s) + 2H33OO++(aq)(aq) Ca Ca 2+2+(aq) + CO(aq) + CO22(g) + (g) +

3H3H22O(l)O(l)

N2(g) + O2(g) 2NO(g)

We can then use We can then use these expressions to these expressions to solve problems. solve problems.

Let’s look at page 506; Let’s look at page 506; problems 1 and 2.problems 1 and 2.

Solubility Product Solubility Product ConstantConstant, K, Kspsp

A special equilibrium constantA special equilibrium constant These are equilibrium constants for These are equilibrium constants for

the the dissolutiondissolution of of slightlyslightly soluble soluble saltssalts It is for describing the It is for describing the saturationsaturation of a of a

salt in solution.salt in solution. The expression is written in the The expression is written in the samesame

way as the other equilibrium way as the other equilibrium constants.constants.

Remember, solids and pure liquids Remember, solids and pure liquids are are notnot included in the expression. included in the expression.

Examples Examples

The KThe Kspsp for silver carbonate is 8.4x10 for silver carbonate is 8.4x10-12-12 at 298. The concentration of carbonate at 298. The concentration of carbonate ions in a saturated solution is 1.28 x 10ions in a saturated solution is 1.28 x 10--

44 M. What is the concentration of silver M. What is the concentration of silver ions?ions?

The ionic substance TThe ionic substance T33UU22 ionizes to form ionizes to form TT2+2+ and U and U3-3- ions. The solubility of T ions. The solubility of T33UU22 is is 3.77 x 103.77 x 10-20-20 mol/L. What is the value of mol/L. What is the value of the solubility-product constant?the solubility-product constant?

Before we work on some Before we work on some problems in Groups, all problems in Groups, all groups to a boardgroups to a board

Part 1) Methane, CHPart 1) Methane, CH44 and water, H and water, H22O, O, react to make carbon monoxide, CO, react to make carbon monoxide, CO, and hydrogen, Hand hydrogen, H22. All are gases. . All are gases. Write the balanced equation.Write the balanced equation.

Part 2) Write the equilibrium expression.Part 2) Write the equilibrium expression.Part 3) Suppose you were given the Part 3) Suppose you were given the

concentrations:concentrations:

HH2 2 = 1.56 M, CH= 1.56 M, CH44 = 3.70 x 10 = 3.70 x 10-2-2 M, H M, H22O = O = 0.827, and the K0.827, and the Keqeq = 3.112 x 10 = 3.112 x 1022. . What is the concentration of CO?What is the concentration of CO?

HomeworkHomework

Page 522-523: 17 (pick 4 of the Page 522-523: 17 (pick 4 of the eight to complete), 27, 28, 31, 35eight to complete), 27, 28, 31, 35