Mar 19-ICE table & Le Chatelier`s principle
Chem 102 Recitation ICE Table in equilibrium calculation & Le Chatelier’s Principles & Weak acids ---Dr. Q. Wang Mar 19, 2015 Initial-Change-Equilibrium Table in K calculations (1) K value; (2) Initial concentration(s); (3) Concentration(s) at equilibrium. Knowing first two, Need to calculate the third. Initial-Change-Equilibrium Table in K calculations Question 1 For the reaction, Kc = 4.0 103 at 1500 K, NiO(s) + CO(g) ⇌ Ni(s) + CO2(g) If a reaction vessel initially contains a mixture of a solid NiO and 0.20 M CO at 1500 K, what is the equilibrium concentration of CO2 at this temperature? Initial-Change-Equilibrium Table in K calculations Question 2 – For the reaction, Kc = 4.0 103 at 1500 K, NiO(s) + CO(g) ⇌ Ni(s) + CO2(g) If a reaction vessel initially contains a mixture of a solid NiO and 0.20 M CO at 1500 K, what is the equilibrium concentration of CO2 at this temperature? NiO(s) + CO(g) ⇌ Ni(s) + CO2(g) Solution: Kc [CO2 ]eq [CO ]eq Assuming at x M of CO will be reacted to reach equilibrium, NiO(s) + CO(g) ⇌ Ni(s) + CO2(g) Kc Initially Change 0.20 M -xM 0M +xM At equilibrium (0.20 - x) M xM x 0.20 x x 0.20M [CO2 ]eq [CO ]eq 4.0 103 Initial-Change-Equilibrium Table in K calculations Question 2 Consider the reaction, Kc = 102 at 500 K, CO(g) + H2O(g) ⇌CO2(g) + H2(g) If a reaction mixture initially contains 0.110 M CO and 0.110 M H2O, what will the equilibrium concentration of each of the reactants and products be? Initial-Change-Equilibrium Table in K calculations Question 3 – Consider the reaction, Kc = 102 at 500 K, CO(g) + H2O(g) ⇌CO2(g) + H2(g) If a reaction mixture initially contains 0.110 M CO and 0.110 M H2O, what will the equilibrium concentration of each of the reactants and products be? Solution: CO(g) + H2O(g) ⇌CO2(g) + H2(g) Kc [CO2 ]eq [ H 2 ]eq [CO ]eq [ H 2O ]eq Assuming at x M of CO will be reacted to reach equilibrium, CO(g) + H2O(g) Kc Initially Change 0.110 M -xM At equilibrium (0.110 - x) M [CO2 ]eq [ H 2 ]eq [CO ]eq [ H 2O ]eq ⇌ 0.110 M -xM (0.110 - x) M x2 102 (0.110 x )2 CO2(g) + H2(g) 0M +xM 0M +xM xM xM 102 At equilibrium, [CO]=[H2O]=0.010 M, [CO2]=[H2]=0.100M x x 0.100M 0.110 x Le Châtelier’s principle • Henri LeChâtelier (1850-1936) • If a system at equilibrium is disturbed by a change in concentration, pressure, or temperature, the system will, if possible, shift to partially counteract the change and restore equilibrium. Le Châtelier’s principle Question 3 This reaction is exothermic. 2 CO(g) ⇌ C(s) + CO2(g) Predict the effect (shift right, shift left, or no effect) of increasing and decreasing the reaction temperature. How does the value of the equilibrium constant depend on temperature? Le Châtelier’s principle Question 3 This reaction is exothermic. 2 CO(g) ⇌ C(s) + CO2(g) (1) Predict the effect (shift right, shift left, or no effect) of increasing and decreasing the reaction temperature. (2) How does the value of the equilibrium constant depend on temperature? Exothermic: 2 CO(g) ⇌ C(s) + CO2(g) + heat If increasing the reaction temperature 2 CO(g) ⇌ C(s) + CO2(g) + heat If decreasing the reaction temperature Le Châtelier’s principle Question 3 This reaction is exothermic. 2 CO(g) ⇌ C(s) + CO2(g) (1) Predict the effect (shift right, shift left, or no effect) of increasing and decreasing the reaction temperature. (2) How does the value of the equilibrium constant depend on temperature? For any equilibrium: If temperature does not change, K will not change. (Changes of volume, pressure, and concentrations will not be able to change K.) Le Châtelier’s principle Question 3 This reaction is exothermic. 2 CO(g) ⇌ C(s) + CO2(g) (1) Predict the effect (shift right, shift left, or no effect) of increasing and decreasing the reaction temperature. (2) How does the value of the equilibrium constant depend on temperature? Exothermic: 2 CO(g) ⇌ C(s) + CO2(g) + heat For an exothermic equilibrium, If T increases, equilibrium shift from products to reactants. K will decrease. If T decreases, equilibrium shift from reactants to products. K will increase. For an endothermic equilibrium, If T increases, equilibrium shift from reactants to products. K will increase. If T decreases, equilibrium shift from products to reactants. K will decrease. Weak Acid Problems Question 4 A 0.200 M solution of a weak acid (HA) has a pH of 2.95. Calculate the acid ionization constant (Ka) for the acid. Weak Acid Problems Question 4 A 0.200 M solution of a weak acid (HA) has a pH of 2.95. Calculate the acid ionization constant (Ka) for the acid. Solution: HA (aq) ⇌ H+(aq) + A-(aq) Ka [ H ]eq [ A ]eq [ HA]eq Assuming at x M of HA will be ionized to reach equilibrium, HA (aq) Initially Change ⇌ 0.200 M -xM At equilibrium (0.200 - x) M Ka [ H ]eq [ A ]eq [ HA]eq x x 0.200 x H+(aq) + A-(aq) 0M +xM 0M +x M xM xM pH 2.95 log[ H ]eq 2.95 [ H ]eq 102.95 1.1 103 M x x (1.110 3 ) 2 1.2 10 6 Ka 6.0 10 6 3 0.200 x 0.200 1.110 0.200 0.0011
© Copyright 2024