1. Ch 14 Chemical equilibrium

2. Reversible reactions and equilibrium
Completion reaction: reaction that proceeds ~100% products
Reversible reaction: when products can reform reactants. <==> (double direction yield signs)
Forward & reverse reactions take place at the same time.
Chemical equilibrium: a state of balance is reached in which the forward reaction rate equals the reverse reaction rate.
[ ] of reactants & products are constant.
Ca 2+ (aq) + SO4 2- (aq) <==> CaSO4(s))

3. Opposing reaction rates
As reactants form products, the [ ] of reactants decrease and the forward rate decreases.
As products are formed the [ ] of products increase and the reverse rate increases.
At equilibrium the rates of the reaction (forward and reverse) are equal & the amount of reactants and products is constant.(pg 498, figure 3)
reactants
Forward Rx:
A + B --> C
Reverse Rx:
C --> A + B
Reaction
rate
equilibrium
products
Time

4. Dynamic chemical equilibrium
Static equilibrium: sate at which nothing changes
Chemical equilibrium is dynamic: no net  in the system yet the process (rate of reaction) occurs at the same time.
Reactants <==> products
Final [ ] of each are not necessarily equal, it is the rates (forward and reverse) that are equal.
Some reactions produce mostly products until reaching equilibrium and some remain mostly reactants when equilibrium is reached.

5. Equilbria/complex ions
Metal ion bonded to more than one atom/ion or molecule.
Bonded molecule/ions are called ligands:
NH3, CN-, OH-, SCN-
All have lone pair of electrons to share with the metal
Transition metals with ligands can be colored (pg 500 table 1)
Charge on complex ion = sum of all the charges.
Cu 2+ (aq) + 4NH3(aq) <==> [Cu(NH3)4]2+

6. System at equilibrium
Equilibrium constant (Keq): when a system is completed (equilibrium) an equilibrium constant (law of mass action) can be written.
Equilibrium constant: a number that indicates equilibrium concentrations of reactants and products at a given temperature. **(s) & (l) are omitted, [ ] does not D
xReactants <==>yProducts
Keq = [P]y/[R]x x & y are coeff. From balanced equation

7. Practice
Write the equilibrium constant equation and calculate the Keq from the [ ] data.
COCl2(g) <==> CO(g) + Cl2(g), equilibrium [ ] are [CO]=[Cl2]=0.0178M and [COCl2]= M
Br2(aq) <==> 2Br(g), equilibrium [ ] are [Br2]=0.99M and [Br]=0.020M
Keq is unit less number
Pg 505 table 2 equilibrium constant at 25oC
Keq >>>1 then mostly products (product favored)
Keq<<<1 then most reactants (reactant favored)
Keq = 1 50/50 mix reactants and products

8. Additional equilibrium problems
Know Keq and equilibrium [ ] of some reactants or products and then calculate the equilibrium [ ] of an unknown.
Determine the equilibrium [ ] of H3O+ and HCO3- in a solution of H2CO3 at 25oC in which [H2CO3] = 0.027M at equilibrium. Keq = 4.3 x H2CO3(aq)<=>H3O+(aq) + HCO3-(aq)
Determine [H2] equilibrium at 700K when [CH3OH]=0.25, [CO]=0.0098, Keq = 290, CO(g) + 2H2(g) <==> CH3OH(g)

9. Solubility product constant Ksp
Maximum [ ] ions of aqueous solute is called a solubility of a salt. (units M)
Ksp (solubility product constant): equilibrium constant for a solid that is in equilibrium with the solid dissolved ions.
AyXb(s) <==> yA+(aq) + bX-(aq)
Ksp = [X-]b/[A+]y
y and b are subscripts from the chemical formula of the salt. Solid not included in equation
Write the Ksp equation for the following salts
PbI2(s), CaSO4(s), Ba3(PO4)2(s)

10. Ksp continue
Salts with low Ksp form ppt when combining 2 solutions with their cation and anion. (pg 508 table 3)
Calculate Ksp from solubility data
s = solubility of salt, [ ] ions = s x # ions in the salt.
Calculate the Ksp of HgI2 if the [Hg 2+ ] in a saturated solution = 1.9 x 10-10M
The Ksp of CdF2 is 6.4 x Calculate the [ ] of the ions in a saturated solution of CdF2

11. Ksp calculations continue
Knowing Ksp and [ ] of know ion, calculate the [ ] of unknown ion.
A chemist wishes to reduce the silver ion [ ] in a saturated AgCl solution to 2.0 x 10-6M. What [ ] of Cl- would achieve this goal?
The Ksp MgCO3 is 6.8 x The [CO32-] ion in a solution containing both MgCO3 and Na2CO3 is 4.0 x What is the [Mg 2+ ] ions if the solution is saturated with respect with to MgCO3?

12. Equilibrium system & stress
Le Chatelier principle: a system in equilibrium will oppose a change in a way that helps eliminate the change, adjust to reduce the change.
Stress: cause a shift in equilibrium until a new equilibrium [ ] is reached.
3 stress: [ ], T and P (gas systems only)
When a stress is added, forward and reverse rates are not equal.
System responds by forming more product or reactant depending on the stress and system until equilibrium is reached again.

13.  [ ]
Increase [ ] of reactant or product => result with a decrease [ ] of reactant or product and proceed to the opposite side of the reaction.
Rate of reaction  until equilibrium is reestablished.
Decrease [ ] of reactants or products just the opposite.
 T
Increase T favors the endothermic reaction direction (+H)
Decrease T favors the exothermic reaction direction (-H)
 P ( involving gases in equilibrium)
Increase pressure (decrease vol) favors the direction of the least # of molecules.
Decrease pressure(increase vol)favors most # molecules
Stresses

14. Common ion effect
Phenomenon in which the addition of an ion common to two solutes brings about a ppt or reduces ionization
Common ion reduces the solubility of a salt.
For the following system determine the shift with the following stresses:
N2(g) + 3H2(g) <==> 2NH3(g) H = +30kJ
Increase T
Decrease P
Add N2 gas