Dynamic Equilibrium
Equilibrium Condition:
· A balance between ______and ______processes
· Constancy of ______, but not ______properties.
· MUST be a ______system
· A system where some of all ______and ______are present
Reaching/Establishing Equilibrium:
· As the reaction ______in the ______direction ( ) ______are converted into ______and the ______of the ______reaction (Ratef) ____ .
· The amount of ______and the rate of the ______reaction ____. ______are converted back to ______which reduces the ______.
· ______, the amount of ______is the ______as ______and ______
Rate / 0.5 / 0.4 / 0.5 / 0.4 / 0.5 / 0.4A / B / A / B / A / B
Exhange # / Amount / Add 20 to A / Remove 13 from A
0 / 70 / 30
Minus
Result
Add
1
Minus
Result
Add
2
Minus / Ratio
Result
Add
Testing for Equilibrium:
· Alter ______such as ______, ______or ______.
· if there is a ______macroscopic change, then the system _____ at ______and is reacting to ______a new equilibrium.
· if there is ____ change then the reaction is ______, or there is no ______at all.
Types of Equilibrium systems:
I) Solubility
II) Phase
III) Chemical Reactions
Percentage Reaction
• all reactions are considered reversible
• the amount of products or reactants can be determined by the % rxn:
If,
% Rxn / Conclusion< 1 %
< 50 %
> 50 %
> 99 %
Percentage Reaction / A2 + B2 D 2AB / Equilibrium Conditions / % rxn
[AB]eq / 1.35 / 1.59 / 2.03
[B2]eq / 0.325 / 0.380 / 0.485
[A2]eq / 0.325 / 0.380 / 0.485
Initial Conditions / [AB]max
[AB]i / 0.00 / 1.35 / 3.00
[B2]i / 1.00 / 0.500 / 0.000
[A2]i / 1.00 / 0.500 / 0.000
ICE Tables
• more ______used to determine ______concentrations, ______than % rxn as [ ]max is not required.
eg. When 0.900 mol of N2 and 2.70 mol of Cl2 are added to a 1.00 L container and allowed to achieve equilibrium, the [Cl2]eq is found to be 0.440 M. Determine the [N2]eq and [NCl3]eq, according to:
N2 + 3 Cl2 D 2 NCl3
Equilibrium Law
1) Equilibrium Constant, Keq:
If, aA + bB D cC + dD
eg. For A2 + B2 D 2AB
2) Significance of Keq magnitude:
· If Keq is ______then is ______and the rxn is ______.
· If Keq is ______then ____ rxn occurs.
3) Keq and the Balanced Chemical Eq’n:
· any ______performed on the chemical rxn, the Keq expression is ______to that ______.
4) Keq and Reaction Kinetics:
If ______
and ______the ______and ______rxns are ______steps, then
______
At equilibrium:
5) Keq & the Effect of Temperature:
· usually ______.
· an ____ in _____ won’t affect the ______and ______reactions ______, so,
______
and the ______will ______
If exothermic:
at ______T an increased ______creates ______than at ______T, and
If endothermic then the ______occurs:
6) Heterogeneous Equilibria:
· reactants and products in different ______states ______
· Pure ______(not aq) and ______have ______densities
· as a result, pure solids and liquids are ______in the ______expression.
eg. 2H2O(l) D 2H2 (g) + O2 (g)
eg. Zn(s) + Cu2+(aq) D Cu (s) + Zn2+(aq)
eg. CaCO3(s) D CaO (s) + CO2 (g)
eg. Zn(s) + 2HCl(aq) D ZnCl2 (s) + H2(g)
Quantitative Changes in Equilibrium Systems
Reaction Quotient, Q
· is a test calculation of the equilibrium system using initial, NOT equilibrium concentrations.
· by comparing the value of Q to Keq, the direction that the equilibrium will change is determined.
If: / Reaction System ResponseQ < Keq
Q = Keq
Q > Keq
eg. Consider the following system:
2 SO2 + O2 D 2 SO3 ; Keq =
a) 2.0 1.0 0 ______
b) 0.50 0.75 1.0 ______
Calculating [ ]eq from [ ]i and Keq
· Write the balanced chemical reaction & Keq.
· Calculate Q to determine the sign of “C” (Change).
· Create an I.C.E. table, input I ( [ ]i ) and C (± nx) and then form the E, ( [ ]eq ) expressions, [ ]i ± nx.
· Substitute [ ]eq expressions into Keq.
· Solve for the unknown, “x”, by using “perfect squares”, 100 Rule, or use the quadratic formula, ().
· Determine [ ]eq values by substituting in the calculated “x” value.
· Check your calculated [ ]eq values by substituting into Q and comparing to Keq.
eg. If 0.100 mol of HCl is placed in a 1.00 L container and allowed to reach equilibrium, find [ ]eq for all species given that Keq = 1.84 x 10-2
eg. If 1.0 mol of NOCl is placed in a 2.0L flask, calculate [ ]eq if Keq= 1.6 x 10-5.
eg. The Keq for the dissociation of I2 into I atoms is
3.80 x 10-2. If the [I2]i is 0.200 M, calculate the [I]eq.
Le Chatelier’s Principle
· An equilibrium under stress will ______in whichever direction ______the stress
· If temperature is ______, Keq is the same ______.
· One ______rxn will ______to ______the stress until
______
and equilibrium is ______
• stresses that ______equilibrium shifts are changes in:
______
______
______
• stress that ______cause an overall equilibrium shift:
adding a ______– both Rrxn f and Rrxn r ______
adding an ______gas – no ______or ______change
eg. A2 (g) + 2 BC (g) « 2 ABC (g) + heat
Effect of change in:
1) Concentration
If a compound’s concentration ______then the equilibrium shifts to the ______side to ______it.
eg. Add _____ then equilibrium _____.
If a compound’s concentration ______then the equilibrium shifts to the _____ side to ______it.
eg. Remove _____ then equilibrium _____.
2) Temperature
If the NRG is ______ then the equilibrium shifts to the ______side to ______ it.
eg. Add ______then equilibrium _____.
If the NRG is ______then the equilibrium shifts to the ______side to ______ it.
eg. Remove _____ then equilibrium ____.
3) Pressure/Volume
eg. A2 (g) + 2 BC (g) « 2 ABC (g) + heat
3 moles gas 2 moles gas
If pressure is ______, volume is ______ then the equilibrium shifts to the side with the ______# of ______.
eg. Add ______, reduce ______, then the equilibrium ______.
If pressure is ______, volume is ______ then the equilibrium shifts to the side with the greater # of particles.
Remove ______, increase ______, then the equilibrium ______.
CoCl42-(al) + 6H2O D Co(H2O)62+ + 4Cl-1 + NRG
stress / Initial change / shift direction / Colored [ ] ¯ / Colored [ ] / visible change2CrO42- + 2H1+ D Cr2O72- + H2O
stress / Initial change / shift direction / Colored [ ] ¯ / Colored [ ] / visible changeN2O4(g) + NRG D 2NO2(g)
stress / Initial change / shift direction / Colored [ ] ¯ / Colored [ ] / visible changeCO2 + H2O D 2H1+ + HCO31-
(with bromothymol blue indicator)
stress / Initial change / shift direction / Colored [ ] ¯ / Colored [ ] / visible change
Solubility Product Constant, Ksp
Solubility:
• is the ______amount of solute in a solvent at a given temperature
• saturated solution, [ ]max
• equilibrium between:
______« ______
eg. AgNO3(s) « Ag1+(aq) + NO31-(aq)
• solubility is a contest between:
• ionic bond strengths vs ______
• lattice energies vs ______
• usually exothermic with ______disorder
• if undissolved solid is present, then it is a ______with a saturated sol’n phase
Solubility Product Constant, Ksp:
• equilibrium expression for slightly soluble salts
If: AxBy(s) « xAm+(aq) + yBn-(aq)
Saturation can be tested by Q:
If: Q = Ksp then: ______
Q > Ksp ______
Q < Ksp ______
Terminology:
• refers to the ______of solid that can dissolve not how much is in ______
• solubility in g/100g or g/100 mL or g/L
To find ______from ______:
[ ]max = ______¸ Msolute x V adjustment
eg. Solubility of Mg(OH)2 is 3.45 g/100mL.
To find ______from ______:
Solubility = ______x Msolute x V adjustment
Calculations:
1) Ksp from solubility
eg. Calculate the Ksp of Ag2CO3 given its solubility of 0.0014 g/100g.
2) Solubility from Ksp
types: solubility, molar solubility, [ion]eq, amount of solid that will dissolve
- all from calculating “x”
eg. How much PbI2 at SATP will dissolve in 1.00 L of water? Give the solute ion concentration, [Pb2+]eq, solubility (g/100mL) and molar solubility.
Predicting Precipitation:
• Used to determine precipitation when mixing 2 sol’ns as with double displacement rxns
eg. Will precipitation occur when 5.0 ml of 0.030 M AgNO3 is mixed with 1.0 ml of 0.0050 M Na2CrO4? (Ksp = 1.1 x 10-12 for Ag2CrO4).
eg. Will 0.10 mg if Ba(OH)2 added to 75 mL of 2.0 x 10-3 M AgNO3 form a precipitate? (Ksp = 1.5 x 10-17 for AgOH).
Common Ion Effect
· Application of Le Chatelier’s Principle to solubility
For: AB2(s) « A2+(aq) + 2 B1-(aq)
the equilibrium can shift in the:
i) ______direction by redissolving solid
ii) ______direction by forming precipitate
Re-dissolving Precipitates
1. Add more solvent
then
For AB « A+ + B-
• A precipitate forms or exists if ______
• Adding solvent it ______the ion concentrations and equilibrium shifts to the ______
2. Addition of an Acid
a) CaCO3(s) « Ca2+ + CO32-
CO32- + 2H+ ® CO2 + H2O
As CO32- falls below ksp
b) Cu(OH)2(s) « Cu2+(aq) + 2OH1-(aq)
H+ + OH- ® H2O
3. Addition of a Complexing Agent
Cu(OH)2 « Cu2+ (down) + 2OH-
Added:
Cu2+(aq) + NH3 ® Cu(NH3)42+
eg. Given that Ksp(AgI) = 4.5 x 10-17, calculate the molar solubility of AgI in:
a) pure water
b) 0.10M NaI
eg. Calculate the molar solubility of AgCl in a 0.20 M CaCl2 solution.
eg. Calculate the solubility, mL/100 mL, of Cr(OH)3 in a 0.15 M Ba(OH)2 solution.