class demo with hall
DESCRIPTION
Definition. Class Demo with hall Chemical Equilibrium – when the rate of the forward and reverse reactions are equal Dynamic – Reactions at eq never stop Equilibrium DOES NOT mean that the amount of reactants and products are equal. They have reached an unchanging ratio. Definition. - PowerPoint PPT PresentationTRANSCRIPT
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Class Demo with hall• Chemical Equilibrium – when the rate of the
forward and reverse reactions are equal• Dynamic – Reactions at eq never stop• Equilibrium DOES NOT mean that the amount of
reactants and products are equal. They have reached an unchanging ratio
Definition
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Equilibrium
Equilibrium GIDefinition
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Cis Trans
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1. NaCl (s) Na+(aq) + Cl-(aq)[unsaturated]
2. NaCl (s) Na+(aq) + Cl-(aq) [saturated]
Definition
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N2O4(g) 2NO2(g)
Clear BrownCold Hot
1. Starting with all reactants (N2O4)
N2O4(g) 2NO2(g)
2. Starting with all products (NO2)
Graphs
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1. Kc = Eq. Constant involving molarity
a. Molarity = [ ]b. Example = [0.50 M]
2. Kp = Eq. Constant involving pressure
a. Atmospheresb. We live at about 1 atm
3. Generic ExampleaA + bB cC + dD
Eq. Constants
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2O3(g) 3O2(g)
2NO(g) + Cl2(g) 2NOCl(g)
H2(g) + I2(g) 2HI(g)
Eq. Constants
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Heterogeneous Equilibrium1. More than one state is present2. Exclude solids and liquids from K. (not
considered to have a molarity or pressure)
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SnO2(s) + 2CO(g) Sn(s) + 2CO2(g)
Pb(NO3)2(aq)+Na2SO4(aq)PbSO4(s)
+2NaNO3(aq)
Ba2+(aq) + SO42-(aq) BaSO4(s)
Heterogeneous Eq.
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1. Exclude liquid water (often the solvent)2. Keep gaseous water3. Examples
CO2(g) + H2(g) CO(g) + H2O(l)
3Fe(s) + 4H2O(g) Fe3O4(s) + 4H2(g)
A Note About Water
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1. An exampleCO(g) + Cl2(g) COCl2(g)
Kc = 4.6 X 109
2. RulesK>>1 Favors the productsK<<1 Favors the reactantsK~1 Reactants ~ Products
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1. Does the following reaction favor the products or reactants?
N2(g) + O2(g) 2NO(g)Kc = 1 X 10-30
2. For the following reaction, Kc = 794 at 298 K and Kc = 54 at 700 K. Should you heat or cool the mixture to promote the formation of HI?
H2(g) + I2(g) 2HI(g)
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1. Kc= 2.5 X 10-30 for N2(g) + O2(g) 2NO(g) calculate Kc for:
2NO(g) N2(g) + O2(g)
2. Calculate Kc for ½ N2(g) + ½ O2(g) NO(g)
3. The Kc for N2(g) + 3H2(g) 2NH3(g) is 4.43 X10-3. Calculate Kc for:
2N2(g) + 6H2(g) 4NH3(g)
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Converting Between Kc and Kp
Kp = Kc (RT)n
R = 0.0821 L atm/mol KT = Kelvin Temperature n = change in number of moles of gas
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Calculate Kp for the following reaction at 300 oC:
N2(g) + 3H2(g) 2NH3(g)
Kc = 9.60
ANS: 0.00434 (4.34 X 10-3)
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Calculate Kp for the following reaction at 1000 K:
2 SO3(g) 2SO2(g) + O2(g)
Kc = 4.08 X 10-3
ANS: 0.335
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1. A mixture is allowed to reach eq.. At eq., the vessel contained 0.1207 M H2, 0.0402 M N2, and 0.00272 M NH3. Calculate the equilibrium constant.
N2(g) + 3H2(g) 2NH3(g)
(Ans: 0.105)
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2. At eq., a vessel contained 0.00106 M NO2Cl, 0.0108 M NO2, and 0.00538 M Cl2. Calculate the equilibrium constant.
NO2Cl(g) NO2(g) + Cl2(g)
(Ans: 0.558)
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3. A mixture of 0.00500 mol of H2 and 0.0100 mol of I2 is placed in a 5.00 L flask and allowed to reach eq.. At eq., the mixture is found to be [HI] = 0.00187 M. Calculate Kc.
H2(g) + I2(g) HI(g)
(Ans: 51)
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4. A vessel is charged with 0.00609 M SO3. At eq., the SO3 concentration had dropped to 0.00244 M SO3. What is the value of Kc?
SO3(g) SO2(g) + O2(g)
(Ans: 0.0041)
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5. 4.00 mol of HI was placed in a 5.00 L flask and allowed to decompose. At eq. It was found that the vessel contained 0.442 mol of I2. What is the value of Kc?
HI(g) H2(g) + I2(g)
(Ans: 0.020)
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6. An eq. mixture of gases is analyzed. The partial pressure of nitrogen is 0.432 atm and the partial pressure of hydrogen is 0.928 atm. If Kp is 1.45 X 10-5, what is the partial pressure of ammonia?
N2(g) + 3H2(g) 2NH3(g)
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7. Consider the following equilibrium:PCl5(g) PCl3(g) + Cl2(g)
a. At equilibrium, the partial pressure of PCl5 and PCl3 are measured to be 0.860 atm and 0.350 atm, respectively. If Kp = 0.497, what is the partial pressure of Cl2? (1.22 atm)
b. Suppose at equilibrium the partial pressure of PCl5 is 2.00 atm. Calculate the partial pressure of PCl3 and Cl2 . Assume Kp is still 0.497 and only PCl5 was initially in the flask. (0.997 atm)
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1. 0 = ax2 + bx + c
2. x = -b + \/ b2 – 4ac2a
3. 2x2 + 4x = 1
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1. A gas cylinder is charged with 1.66 atm of PCl5 and allowed to reach eq.. If the Kp= 0.497, what are the pressures of all the gases at equilibrium?
PCl5(g) PCl3(g) + Cl2(g)
(Ans: 0.97 atm, 0.693 atm)
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2. A 1.000 L flask is filled with 1.000 mol of H2 and 2.000 mol of I2. The Kc = 50.5. What are the concentrations of all the gases at equilibrium?
H2(g) + I2(g) 2HI(g)
(Ans: 0.065 M, 1.065 M, 1.87 M)
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Do I always need the quadratic, or can I cheat?
The equilibrium constant for the following reaction is 2400.
2NO(g) N2(g) + O2(g)
If the initial concentration of NO is 0.157 M, calculate the equilibrium concentrations of NO, N2 and O2.
(Ans: 0.0016 M, 0.0777 M, 0.0777 M)
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Equilibrium
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1. Reaction Quotient2. Calculated the same as K, but using initial
concentrations
3. Q < Kshifts to productsQ = Kat equilibriumQ > Kshifts to reactants
Q: Reaction Quotient
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1. If you introduce 0.0200 mol of HI, 0.0100 mol of H2 and 0.0300 mol of I2 in a 2.00 L flask, which way will the reaction proceed to reach equilibrium?
H2(g) + I2(g) 2HI(g) Kc = 51
(Ans: Q = 1.3)
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2. Predict which way the following reaction will proceed as it reaches eq. Assume that you start with [SO3] = 0.002 M, [SO2] = 0.005 M and [O2] = 0.03M.
2SO3(g) 2SO2(g) + O2(g)
Kc = 0.0041
(Ans: Q = 0.2)
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3. Predict which way the following reaction will proceed as it reaches eq. Assume that you start with [NH3] = 0.002 M, [N2] = 0.005 M and no H2. Kc= 0.105
N2(g) + 3H2(g) 2NH3(g)
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Blue Bottle Demo5 grams KOH3 grams Dextrose250 mL of water1 drop methylene blue
LeChatelier’s Principle
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• Definition – If a system at eq. Is disturbed, it will shift to relieve that disturbance
LeChatelier’s Principle
If a system at eq. is disturbed, it
will shift to relieve that disturbance
Le’Chatelier’s Principle
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N2(g) + 3H2(g) 2NH3(g)
• Add N2
• Add NH3
• Remove NH3 as it forms• Remove H2
N.B. Does NOT apply to solids and liquids. They do not appear in the K.
LiCl(s) Li+(aq) + Cl-(aq)
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Disturbing and K
• Adding products = K increases (TEMPORARILY)• Adding reactants = K decreases
(TEMPORARILY)
N2(g) + 3H2(g) 2NH3(g)
Kc = [NH3]2 [N2][H2]3
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N2(g) + 3H2(g) 2NH3(g)
• Identify the # of moles of gas on either side.• Show piston drawing
1. Increase the volume of the container2. Decrease the volume of the container
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N2(g) + 3H2(g) 2NH3(g)
1. Increase the pressure of the system2. Decrease the pressure of the system
Soda example (CO2(aq) CO2(g))
N.B. Adding a noble or inert gas has no effect on the eq. Pressure change without a volume change.
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• Endothermic Reactions – absorb heat from the surroundings– Heat is added (reactants)– Cooking is an example
H +
• Exothermic Reactions – Release heat– Give off heat (products)– Fire is an example
H -
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CO(g) + 3H2(g) CH4(g) + H2O(g)
H = -206 kJ/mol
1. Heat the system2. Cool the system
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1. Catalyst2. Examples
a. Enzymesb. Vitaminsc. Catalytic convertor
3. No effect on the position of equilibrium
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Example 1N2O4(g) 2NO2(g)
H = 58 kJ/mol
a. Add N2O4
b. Remove NO2 as it formsc. Increase the total pressured. Increase the total volumee. Cool the solutionf. Add a catalyst
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Example 2.
2PbS(s) + 3O2(g) 2PbO(s) + 2SO2(g)H = -37 kJ/mol
a. Add PbSb. Remove SO2 as it formsc. Add O2d. Increase volumee. Decrease the pressuref. Heat the flask
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Example 3.Given the following eqn., how could you promote the
formation of PCl3 and Cl2?
PCl5(g) PCl3(g) + Cl2(g)H = 88 kJ/mol
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Example 4.How could you promote the formation of CH4?
CO(g) + 3H2(g) CH4(g) + H2O(g) H = -206 kJ/mol
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SINGLE ARROWReaction goes to completion
HCl + NaOH NaCl + H2O
ICEnd
Na+ Cl-
H2O
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Double ARROWReaction goes to equilibrium (all species present)
N2 + 3H2 2NH3
ICEquilibrium
N2 H2 K = [NH3]2 ratio
NH3 [N2][H2]3
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HC2H3O2(aq) + H2O(l) ↔ H3O+(aq) + C2H3O2-(aq)
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Fe3+(aq) + SCN-(aq) ↔ FeSCN2+(aq)
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Co(H2O)62+(aq) + 4Cl-(aq) + 50 kJ/mol ↔ CoCl4
2-(aq) + 6H2O(l)
(pink) (blue)
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NaCl(s) ↔ Na+(aq) + Cl-(aq)
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14.[O2]3/[O3]2 1/[Cl2]2
[C2H6]2[O2]/[C2H4]2[H2O]2 [CH4]/[H2]2
[Cl2]2/[HCl]4[O2]16. a) Products b) Reactants 18. Kc = 85820a) 1.35 X 105 b) H2S favored22a) 13.3 b) 0.274 c) 0.034926. Kp = 1/PSO2
Na2O is a solid, no molarity or pressure28. Kc = 10.530. 66.8, Products favored32. a) 0.14 M, 0.020 M, 0.40 M b) 58
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38. a) 0.0013(R) b) Reactants c) 1.1 X10-5(P) 40.0.0535 atm42a. 0.0362 g I2 b) 0.018 g SO2
44. 0.13 M46.0.011 M48a. 0.0432 M PH3 and BCl3
52 a) increase(P) b) decrease(R) c) decrease(R)d) decrease(R) e) no change f) decrease(R)
54 a) Endothermic b) more moles of gas in product56 a) -90.7 kJ b) exothermic
c) Increase pressure 59. Kp = 24.7 Kc = 0.00367
60. 0.71
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Take-Home Pretest1.1.09 g NaOH2.20.43.43524.1675.Products6.Q = 0.637, moves to products7.[H2] = 0.312 M, [Cl2] = 0.012 M, [HCl] = 0.376 M
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Equilibrium
1.82 = 2m log 1.82 = log 2m log 1.82 = m log 2
0.260 = 0.301 mm = 0.864