Honors Chemistry. Chapter 18: Equilibrium Worksheet Date / / Period

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1 Honors Chemistry Name Chapter 18: Equilibrium Worksheet Date / / Period 1. Write the expressions for the equilibrium constant K c and indicate if the reactions are homogeneous equilibriums or s for the following reactions: a. 4 NH 3(g) + 7 O 2(g) 4 NO 2(g) + 6 H 2 O ( ) K c = [NO 2 ] 4 [NH 3 ] 4 [O 2 ] 7 b. HCN (aq) + H 2 O ( ) H 3 O +1 (aq) + CN -1 (aq) K c = [H 3 O +1 ][CN -1 ] [HCN] c. PCl 5(g) + PCl 3(g) + Cl 2(g) K c = [PCl 3 ][Cl 2 ] [PCl 5 ] homogeneous equilibrium d. CaCO 3(s) CaO (s) + CO 2(g) K c = [CO 2 ] e. 3 O 2(g) 2 O 3(g) K c = [O 3 ] 2 [O 2 ] 3 homogeneous equilibrium f. 2 H 2 O ( ) H 3 O + (aq) + OH -1 (aq) K c = [H 3 O + ][OH -1 ] g. 3 Zn (s) + 2 Fe +3 (aq) 2 Fe (s) + 3 Zn +2 (aq) K c = [Zn +2 ] 3 [Fe +3 ] 2 2. Write the equilibrium constant expressions for the following reactions. How are they related to one another? a. 2 N 2 O (g) + 3 O 2(g) 4 NO 2(g) K = [ NO 2 ] 4 a is the inverse of c. [N 2 O] 2 [O 2 ] 3 b. N 2 O (g) + 3 / 2 O 2(g) 2 NO 2(g)

2 K = [ NO 2 ] 2 b contains ½ as many moles as a. [N 2 O][O 2 ] 3/2 c. 4 NO 2(g) 2 N 2 O (g) + 3 O 2(g) K = [ N 2 O] 2 [O 2 ] 3 c is the inverse of a. [NO 2 ] 4 3. Calculate the value of the equilibrium constant for the following system, given the data shown: H 2(g) + CO 2(g) Concentrations at equilibrium: [H 2 ] = 1.5 mol Liter -1 [CO 2 ] = 2.5 mol Liter -1 [H 2 O] = 0.5 mol Liter -1 [CO] = 3.0 mol Liter -1 H 2 O (g) + CO (g) K = [H 2 O][CO] = [0.5][3.0] = 0.4 [H 2 ][CO 2 ] [1.5][2.5] 4. The following reaction is exothermic: Ti (s) + 2 Cl 2(g) TiCl 4(g) List all the ways the yield of the product TiCl 4 could be increased. 1. Increase the concentration of Ti (s). 2. Increase the concentration of Cl 2(g). 3. Remove TiCl 4(g). 4. Increase the pressure. 5. Decrease the temperature. 5. What three things must be taken into account when determining if a reaction has enough energy to overcome the activation energy (E a )? 1. Temperature 2. Pressure 3. Concentration 6. What does a catalyst do to a reaction? Explain. It speeds up the reaction but is NOT consumed in the process. It helps an equilibrium reaction reach its equilibrium more quickly. 7. What does it mean when an equilibrium system is described as a dynamic system? Explain. Is a system in which the concentrations of reactants and products do not change even though forward and reverse reactions are occurring.

3 8. Draw a diagram for activation energy that indicates that the reaction is endothermic and one that indicates that the reaction is exothermic. Label the x-axis, y-axis, reactants, products, and what amount of activation energy is needed for each reaction. 9. What does the K sp value indicate about an ionic solid? The K sp value indicates how well an ionic compound will dissolve in water and can also be used to determine if a precipitate is formed at a given temperature. 10. For the reaction 2 N 2(g) + O 2(g) 2 N 2 O (g) it is found that, at equilibrium at a particular temperature, the concentrations of reactants and products are: [N 2(g) ] = 1.41 x 10-4 M; [O 2(g) ] = 1.25 x 10-5 M; [N 2 O (g) ] = 1.01 x 10-2 M. Calculate the value of the equilibrium constant K for the reaction at this temperature. K = [N 2 O] 2 = [1.01 x 10-2 ] 2 = 4.10 x 10 8 [N 2 ] 2 [O 2 ] [1.41 x 10-4 ] 2 [ 1.25 x 10-5 ] 11. For the reaction 2 H 2 O (g) 2 H 2(g) + O 2(g) K = 2.4 x 10-3 at a given temperature. At equilibrium it is found that [H 2 O] = 1.1 x 10-1 M and [H 2 ] = 1.9 x 10-2 M. What is the concentration of O 2(g) under these conditions? K = [O 2 ][ H 2 ] 2 [O 2 ] = K [H 2 O] 2 = (2.4 x 10-3 )[1.1 x 10-1 ] 2 = 8.0 x 10-2 M [H 2 O] 2 [H 2 ] 2 [1.9 x 10-2 ] 2

4 12. Approximately 1.5 x 10-3 g of Iron II hydroxide, Fe(OH) 2(s), dissolves per liter of water at 18 o C. Calculate the K sp for Fe(OH) 2(s) at this temperature. H 2O Fe(OH) 2(s) Fe +2 (aq) + 2 (OH) -1 (aq) 1.5 x 10-3 g Fe(OH) 2 1 moles Fe(OH) 2 = 1.7 x 10-5 moles Fe(OH) 2 = 1.7 x 10-5 M Fe(OH) g Fe(OH) 2 1 L 1.7 x 10-5 moles Fe(OH) 2 1 moles Fe +2 = 1.7 x 10-5 moles Fe +2 = 1.7 x 10-5 M Fe +2 1 moles Fe(OH) 2 1 L 1.7 x 10-5 moles Fe(OH) 2 2 moles (OH) -1 = 3.4 x 10-5 moles (OH) -1 = 3.4 x 10-5 M (OH) -1 1 moles Fe(OH) 2 1 L K sp = [1.7 x 10-5 ][ 3.4 x 10-5 ] 2 = 2.0 x Magnesium fluoride dissolves in water to the extent of 8.0 x 10-2 g/l at 25 o C. Calculate the solubility of MgF 2(s) in moles per liter, and calculate the K sp for MgF 2(s) at 25 o C. H 2O MgF 2(s) Mg +2 (aq) + 2 F -1 (aq) 8.0 x 10-2 g MgF 2 1 mole MgF 2 = 1.3 x 10-3 M MgF 2 1 L g MgF x 10-3 mole MgF 2 1 mole Mg +2 = 1.3 x 10-3 M Mg +2 1 L 1 mole MgF x 10-3 mole MgF 2 2 mole F -1 = 2.6 x 10-3 M F -1 1 L 1 mole MgF 2 K sp = [Mg +2 ][ F -1 ] 2 = [1.3 x 10-3 ][ 2.6 x 10-3 ] 2 = 8.8 x For the reaction N 2(g) + O 2(g) 2 NO (g) the equilibrium constant K has the value 1.71 x 10-3 at a particular temperature. If the concentrations of both N 2(g) and O 2(g) are M in an equilibrium mixture at this temperature, what is the concentration of NO (g) under these conditions? K = [NO] 2 = [NO] = K[O 2 ][ N 2 ] = (1.71 x 10-3 )[ ][ ] = 1.41 x 10-3 M [O 2 ][ N 2 ] 15. Consider the equilibrium PCl 3(g) + Cl 2(g) PCl 5(g). How would the following changes affect the partial pressures (concentration) of each gas at equilibrium? PCl 3(g) + Cl 2(g) PCl 5(g) a) addition of PCl b) removal of Cl 2 + c) removal of PCl 5 d) decrease in the volume of the container + e) addition of He without change in volume NO CHANGE

5 16. Indicate how each of the following changes affects the amount of each gas in the system below, for which H reaction = +9.9 kcal kcal + H 2(g) + CO 2(g) H 2 O (g) + CO (g) a) addition of CO b) addition of H 2 O c) addition of a catalyst NO CHANGE d) increase in temperature + + e) decrease in the volume of the container NO CHANGE 17. Consider the equilibrium: 2N 2 O (g) + O 2(g) 4NO (g) How will the amount of chemicals at equilibrium be affected by 2 N 2 O (g) + O 2(g) 4 NO (g) a) adding N 2 O + + b) removing O 2 + c) increasing the volume of the container + d) adding a catalyst NO CHANGE 18. For the reaction, 4 NH 3(g) + 3 O 2(g) 2 N 2(g) + 6 H 2 O (l) How will the concentration of each chemical be affected by 4 NH 3(g) + 3 O 2(g) 2 N 2(g) + 6 H 2 O (l) a) adding O 2 to the system b) adding N 2 to the system c) removing H 2 O from the system + d) decreasing the volume of the container + + There will be one question like number 19 on the quiz. 19. When ammonia is dissolved in water, the following equilibrium is established. If the equilibrium constant is 1.8 x 10-5, calculate the hydroxide ion concentration in the solution if mole of ammonia is dissolved in sufficient water to make 500 ml of solution. NH 3(aq) + H 2 O (l) NH 4 +1 (aq) + OH -1 (aq) I M 0 0 x + x + x Assume = M x M Eq M x x x K b = [NH 4 +1 ][ OH -1 ] [NH 3 ] 1.8 x 10-5 = x 2 [0.200] x = [NH 4 +1 ] = [OH -1 ] = M