1. The Haber- Bosch Process 2. K eq

Transcription

1 Chemistry 12 Equilibrium III Name: Date: Block: 1. The Haber- Bosch Process 2. K eq The Haber- Bosch Process Almost all of the world s ammonia is produced via the Haber- Bosch process and almost all of our inorganic nitrogen compounds are produced from this ammonia. More than 100 million tonnes of ammonia with a value in excess of $600 million are produced annually. About 80% of the world s ammonia is used to produce fertilizers. Other products include explosives, plastics, fibres and dyes. German chemist Fritz Haber developed the equipment and procedures from producing ammonia (NH 3) from its constituent elements (N 2 and H 2) in In 1918, he received the Nobel Prize in chemistry for his accomplishment. In 1931, another German chemist, Carl Bosch, won the Nobel Prize in chemistry, in part for transforming the process to an industrial scale. The balanced equation and enthalpy for the reaction are: N 2(g) + 3 H 2 (g) 2 NH 3 (g) ΔH= - 92 kj/mol The Equilibrium Constant Consider the following equation: N 2(g) + 3 H 2 (g) 2 NH 3 (g) At equilibrium, the forward and reverse rates are equal. Forward rate: Reverse rate: Rearranging to isolate the constants, we get: In this case, k f k r provides a constant that chemists call the equilibrium constant, K eq. K eq =

2 Regardless of the initial concentrations of reactants and products, when equilibrium is achieved and the equilibrium concentrations are substituted into this expression, the calculated value will always be the same. The equilibrium law states that for the general balanced equation: a A + bb c C + d D Balance and write the equilibrium expression for the following reactions: C 2H 2(g) + H 2 (g) CH 4(g) SO 2(g) + O 2 (g) SO 3 (g) HCl (g) + O 2 (g) Cl 2(g) + H 2O (g) CH 4(g) + H 2O (g) CO (g) + H 2 (g) 1. The following gases are at equilibrium in a flask at 423 o C: 4.56 x 10-3 M H 2, 7.4 x 10-4 M I 2, and 1.35 x 10-2 M HI. What is the equilibrium constant for the reaction at this temperature? H 2 (g) + I 2 (g) HI (g) 2. A quantity of 3.88 x 10-3 M NO 2 is at equilibrium with 1.73 x 10-4 M N 2O 4 at 60 o C. What is the equilibrium constant for the reaction? NO 2 (g) N 2O 4(g)

3 Chemicals in liquids or solid states are not included in the equilibrium expressions. Liquids and solids have a fixed density and therefore, a fixed concentration. The only exception is when two liquids appear in the same equation, thus each liquids dilutes the other. Balance and write the equilibrium expression for the following reactions: Cr 2O 7-2 (aq) + H 2O (l) H + (aq) + CrO 4 2- (aq) NaCl (s) Na + (aq) + Cl - (aq) H 2(g) + Br 2 (l) HBr (g) B 2H 6(g) + O 2 (g) B 2O 3(s) + H 2O (g) Hebden Workbook: Pg. 60 #31, 34, 35:

4 Size of K eq Recall that K eq = [products] [reactants] The size of the equilibrium constant is affected by the extent to which the reaction shifts to the left or right to achieve equilibrium. K eq>1 are favoured. K eq<1 are favoured. Changing the is the only way to change a chemical equation s equilibrium constant. Consider the following equation: N 2(g) + 3 H 2 (g) 2 NH 3 (g) ΔH= - 92 kj/mol This is an thermic reaction. (Remember, heat is thought of as an invisible product or reactant) When the temperature is increased, [reactants] and [products]. For the following equations, state whether the K eq would increase or decrease: Equation: Temperature change: K eq result: G + H J ΔH= - 92 kj/mol Increase A + B + heat C Increase P + Q R + S kj Decrease W + X kj Y + Z Decrease N + M P ΔH= +125 kj/mol Increase

5 For the following equations, determine whether the reaction is endothermic or exothermic from the observations: Equation: Temperature Change: Keq: Exo or Endo: A + B C + D Increase Increases E + F G + H Decrease Decrease I + J K + L Increase Decrease M + N O + P Decrease Increase Q + R S + T Increase Decrease For the following equations, determine whether the temperature has increased or decreased: Equation: K eq result: Temperature change: G + H J ΔH= - 92 kj/mol Increased A + B + heat C Decreased P + Q kj R + S Increased W + X kj Y + Z Decreased N + M P ΔH= +125 kj/mol Increased

6 Practice Questions: 1. Balance and write the equilibrium expression for each of the following: a. Fe (s)+ H + (aq) H 2 (g) + Fe 2+ (aq) b. I - (aq) + Cl 2 (aq) I 2 (s) + Cl - (aq) c. CaO (s) + CO 2 (g) CaCO 3 (s) d. CO 2 (g) CO 2 (aq) e. Na 2O (s) Na (l) + O 2 (g) 2. A 2.0 L flask contains 0.38 mol CH 4(g), 0.59 mol C 2H 2(g), and 1.4 mol H 2(g) at equilibrium. Calculate the equilibrium constant for the reaction: CH 4(g) C 2H 2 (g)+ H 2 (g)

7 3. A cylinder contains 0.12 M CoBr 2, M CO, and M Br 2 at equilibrium. The volume of the cylinder is suddenly doubled. COBr 2(g) CO (g) + Br 2 (g) a) What is the molar concentration of each gas immediately after the volume of the cylinder is doubled? b) Explain, in terms of Le Chatelier s principle, why the system shifts right to restore equilibrium. 4. A closed flask contains 0.65 mol/l N 2 and 0.85 mol/l H 2 at equilibrium. What is the [NH 3]? N 2 (g) + 3 H 2 (g) 2 NH 3 (g) K eq = Hebden Workbook: Pg. 62 #36-46: