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 Equilibrium GI

Cis Trans

Definition NaCl (s)  Na+(aq) + Cl-(aq) [unsaturated] NaCl (s)  Na+(aq) + Cl-(aq) [saturated]

Graphs 2. Starting with all products (NO2) N2O4(g)  2NO2(g) Clear Brown Cold Hot Starting with all reactants (N2O4) 2. Starting with all products (NO2) Graphs

Eq. Constants Kc = Eq. Constant involving molarity a. Molarity = [ ] b. Example = [0.50 M] 2. Kp = Eq. Constant involving pressure a. Atmospheres b. We live at about 1 atm Generic Example aA + bB  cC + dD

Eq. Constants 2O3(g)  3O2(g) 2NO(g) + Cl2(g)  2NOCl(g) H2(g) + I2(g)  2HI(g)

Heterogeneous Equilibrium More than one state is present Exclude solids and liquids from K. (not considered to have a molarity or pressure)

Heterogeneous Eq. SnO2(s) + 2CO(g)  Sn(s) + 2CO2(g) Pb(NO3)2(aq)+Na2SO4(aq)PbSO4(s) +2NaNO3(aq) Ba2+(aq) + SO42-(aq)  BaSO4(s)

A Note About Water Exclude liquid water (often the solvent) Keep gaseous water Examples CO2(g) + H2(g)  CO(g) + H2O(l) 3Fe(s) + 4H2O(g)  Fe3O4(s) + 4H2(g)

An example CO(g) + Cl2(g)  COCl2(g) Kc = 4.6 X 109 Rules K>>1 Favors the products K<<1 Favors the reactants K~1 Reactants ~ Products

Does the following reaction favor the products or reactants? N2(g) + O2(g)  2NO(g) Kc = 1 X 10-30 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)

Kc= 2.5 X 10-30 for N2(g) + O2(g)  2NO(g) calculate Kc for: 2NO(g)  N2(g) + O2(g) 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)

Converting Between Kc and Kp Kp = Kc (RT)Dn R = 0 Converting Between Kc and Kp Kp = Kc (RT)Dn R = 0.0821 L atm/mol K T = Kelvin Temperature Dn = change in number of moles of gas

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)

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

A mixture is allowed to reach eq. At eq. , the vessel contained 0 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)

2. At eq. , a vessel contained 0. 00106 M NO2Cl, 0. 0108 M NO2, and 0 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)

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)

4. A vessel is charged with 0. 00609 M SO3. At eq 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)

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)

An eq. mixture of gases is analyzed 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)

PCl5(g)  PCl3(g) + Cl2(g) Consider the following equilibrium: PCl5(g)  PCl3(g) + Cl2(g) 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) 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)

0 = ax2 + bx + c x = -b + \/ b2 – 4ac 2a 2x2 + 4x = 1

1. A gas cylinder is charged with 1 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)

2. A 1. 000 L flask is filled with 1. 000 mol of H2 and 2 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)

Do I always need the quadratic, or can I cheat 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)

Q: Reaction Quotient Reaction Quotient Calculated the same as K, but using initial concentrations 3. Q < K shifts to products Q = K at equilibrium Q > K shifts to reactants

If you introduce 0. 0200 mol of HI, 0. 0100 mol of H2 and 0 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)

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)

Predict which way the following reaction will proceed as it reaches eq 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)

LeChatelier’s Principle Blue Bottle Demo 5 grams KOH 3 grams Dextrose 250 mL of water 1 drop methylene blue

Le’Chatelier’s Principle If a system at eq. is disturbed, it will shift to relieve that disturbance Definition – If a system at eq. Is disturbed, it will shift to relieve that disturbance

LiCl(s)  Li+(aq) + Cl-(aq) 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)

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

N2(g) + 3H2(g)  2NH3(g) Identify the # of moles of gas on either side. Show piston drawing Increase the volume of the container Decrease the volume of the container

N2(g) + 3H2(g)  2NH3(g) Increase the pressure of the system 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.

Endothermic Reactions – absorb heat from the surroundings Heat is added (reactants) Cooking is an example DH + Exothermic Reactions – Release heat Give off heat (products) Fire is an example DH -

DH = -206 kJ/mol Heat the system Cool the system CO(g) + 3H2(g)  CH4(g) + H2O(g) DH = -206 kJ/mol Heat the system Cool the system

Catalyst Examples a. Enzymes b. Vitamins c. Catalytic convertor 3. No effect on the position of equilibrium

Example 1 N2O4(g)  2NO2(g) DH = 58 kJ/mol Add N2O4 Remove NO2 as it forms Increase the total pressure Increase the total volume Cool the solution Add a catalyst

Example 2. DH = -37 kJ/mol Add PbS Remove SO2 as it forms Add O2 2PbS(s) + 3O2(g)  2PbO(s) + 2SO2(g) DH = -37 kJ/mol Add PbS Remove SO2 as it forms Add O2 Increase volume Decrease the pressure Heat the flask

Example 3. Given the following eqn Example 3. Given the following eqn., how could you promote the formation of PCl3 and Cl2? PCl5(g)  PCl3(g) + Cl2(g) DH = 88 kJ/mol

CO(g) + 3H2(g)  CH4(g) + H2O(g) Example 4. How could you promote the formation of CH4? CO(g) + 3H2(g)  CH4(g) + H2O(g) DH = -206 kJ/mol

SINGLE ARROW Reaction goes to completion HCl + NaOH  NaCl + H2O I C End Na+ Cl- H2O

Double ARROW Reaction goes to equilibrium (all species present) N2 + 3H2  2NH3 I C Equilibrium N2 H2 K = [NH3]2 ratio NH3 [N2][H2]3

HC2H3O2(aq) + H2O(l) ↔ H3O+(aq) + C2H3O2-(aq)

Fe3+(aq) + SCN-(aq) ↔ FeSCN2+(aq)

Co(H2O)62+(aq) + 4Cl-(aq) + 50 kJ/mol ↔ CoCl42-(aq) + 6H2O(l) (pink) (blue)

NaCl(s) ↔ Na+(aq) + Cl-(aq)

[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 = 858 20a) 1.35 X 105 b) H2S favored 22a) 13.3 b) 0.274 c) 0.0349 26. Kp = 1/PSO2 Na2O is a solid, no molarity or pressure 28. Kc = 10.5 30. 66.8, Products favored 32. a) 0.14 M, 0.020 M, 0.40 M b) 58

38. a) 0.0013(R) b) Reactants c) 1.1 X10-5(P) 0.0535 atm 42a. 0.0362 g I2 b) 0.018 g SO2 0.13 M 0.011 M 48a. 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 product 56 a) -90.7 kJ b) exothermic c) Increase pressure 59. Kp = 24.7 Kc = 0.00367 60. 0.71

Take-Home Pretest 1.09 g NaOH 20.4 4352 167 Products Q = 0.637, moves to products [H2] = 0.312 M, [Cl2] = 0.012 M, [HCl] = 0.376 M

1.82 = 2m log 1.82 = log 2m log 1.82 = m log 2 0.260 = 0.301 m m = 0.864