Chemical Kinetics and Equilibrium

Transcription

1 Chemical Kinetics and Equilibrium 1 Which statement incorrectly describes a chemical reaction approaching equilibrium? As a chemical reaction approaches equilibrium, the net change in the amount of reactants and products approaches 0 The rate of the reverse reaction increases quickly, then increases slowly until it becomes constant The reactant concentrations decrease quickly, then decrease slowly until they become constant The product concentrations increase quickly, then increase slowly until they become constant The rate of the forward reaction decreases until it attains a value of 0 2 A closed flask is set up in which only substance C is present with an initial concentration of 080 M When a state of equilibrium is reached in the reaction C D + 2E, the equilibrium concentration of C is 020 M What are the equilibrium concentrations of D and E? [D] = 060 M and [E] = 030 M [D] = 060 M and [E] = 12 M [D] = 060 M and [E] = 060 M [D] = 020 M and [E] = 040 M [D] = 020 M and [E] = 010 M 3 Which expression is correct for the reaction CH 4 (g) + 2H 2 O(g) CO 2 (g) + 4H 2 (g)? K c = [CO 2 ][H 2 ] 4 /[CH 4 ][H 2 O] 2 K c = [CH 4 ][H 2 O]/[CO 2 ][H 2 ] K c = [CO 2 ](2 x [H 2 ])/[CH 4 ](4 x [H 2 O]) K c = [CO 2 ][H 2 ]/[CH 4 ][H 2 O] K c = [CH 4 ][H 2 O] 2 /[CO 2 ][H 2 ] 4 4 If K c = 26 x at 100 C for the reaction 2SO 2 (g) + O 2 (g) 2SO 3 (g), then what is the value of K c for the reaction 2SO 3 (g) 2SO 2 (g) + O 2 (g)? 38 x 10 16

2 16 x x x x Which expression correctly relates K p to K c for the reaction 2A(g) + B(g) C(g)? K p = K c (RT) -1 K p = K c (RT) -2 K c = K p (RT) -2 K p = K c /(RT) -2 K p = K c (RT) 2 6 What is the value of K p for the reaction CO(g) + Cl 2 (g) COCl 2 (g) at 800 K if P CO = 075 atm, P Cl2 = 21 atm, and P COCl2 = 150 atm?] Which statement best explains why solids and liquids are not included in equilibrium expressions? Concentrations of solids and liquids are constants The vapor pressure of solids and liquids = 0 atm Concentrations of solids and liquids = 0 in equilibrium expressions Concentrations of solids and liquids = 1 M Concentrations of solids and liquids cancel in the equilibrium expression 8 Which statement is true for an equilibrium system having a K c = 1 x 10-21? [ At equilibrium the reactant and product concentrations will be appreciable At equilibrium the amount of products present will be very small relative to the amount of reactants The reaction will proceed to completion

3 The equilibrium ratio of products to reactants is inversely proportional to the equilibrium constant At equilibrium the amount of reactants present will be very small relative to the amount of products present 9 A mixture of 20 moles of H 2 S, 20 moles of H 2, and 10 mole of S 2 is placed in a 100 L container Which statement is true if the reaction 2H 2 S(g) 2H 2 (g) + S 2 (g) has a K c = 103 x 10-6 at 750 C? The reaction goes from left to right to attain an equilibrium state The reaction is already at equilibrium The concentrations of the products will decrease, while the concentration of the reactant will increase to attain an equilibrium state The equilibrium ratio of products to reactants will decrease The concentrations of H 2 S and H 2 will decrease since they are larger than the concentration of S 2 10 What are the equilibrium concentrations [I 2 ] and [I] for the reaction I 2 (g) 2I(g) if the initial concentrations are 20 x 10-6 M I 2, 0 M I, and K c = 40 x 10-8? [I 2 ] = 17 x 10-6 M and [I] = 26 x 10-7 M [I 2 ] = 19 x 10-6 M and [I] = 27 x 10-7 M [I 2 ] = 19 x 10-6 M and [I] = 14 x 10-7 M [I 2 ] = 20 x 10-6 M and [I] = 40 x 10-6 M [I 2 ] = 20 x 10-6 M and [I] = 80 x M 11 A mixture of CO 2, CO, and C placed in a 100 L container is allowed to come to equilibrium according to the reaction CO 2 (g) + C(s) 2CO(g) Which action does not have an effect on the concentrations of materials found in the equilibrium expression? increasing the volume adding C removing CO increasing the temperature adding CO 2

4 12 Which procedure will shift the equilibrium reaction A(g) + 2B(g) + D(g) from right to left? removing B adding B adding A removing C removing D C(g) 13 Which concentration stress is correctly matched to the relationship between Q c and K c for the equilibrium reaction CH 3 OH(g) CO(g) + 2H 2 (g) adding CO : Q c < K c removing CH 3 OH : Q c < K c adding CH 3 OH : Q c < K c removing CO : Q c > K c adding H 2 : Q c < K c 14 Which reaction will shift to the right when the pressure is decreased by increasing the volume? [Hint] C(s) + CO 2 (g) 2CO(g) 2HI(g) H 2 (g) + I 2 (g) PCl 3 (g) + Cl 2 (g) Fe 2 O 3 (s) + 3CO(g) N 2 (g) + 3H 2 (g) PCl 5 (g) 2NH 3 (g) 2Fe(l) + 3CO 2 (g) 15 Which equilibrium is correctly matched to the shift in reaction when the pressure is decreased by increasing the volume? C 6 H 12 (g) C 6 H 6 (g) + 3H 2 (g) : shifts right to left Cl 2 (g) + 2NO 2 (g) PBr 3 (g) + Br 2 (g) H 2 O(g) + CH 4 (g) Cu 2 O(s) + H 2 (g) 2ClNO 2 (g) : shifts left to right PBr 5 (g) : shifts left to right CO(g) + 3H 2 (g) : shifts left to right 2Cu(s) + H 2 O(g) : shifts left to right 16 Which statement is correct concerning the relationship of the equilibrium constant to temperature?

5 The equilibrium constant for a reaction is independent of temperature The equilibrium constant for an exothermic reaction decreases as the temperature increases If the heat of reaction is negative for a given reaction, then the equilibrium constant for that reaction will increase with increasing temperature If the heat of reaction is positive for a given reaction, then the equilibrium constant for that reaction will decrease with increasing temperature The equilibrium constant for an endothermic reaction decreases as the temperature increases 17 Which relationship between catalysts and equilibrium reactions is correct? [ A catalyst lowers the heat of reaction A catalyst increases the amount of products in an equilibrium reaction A catalyst increases the value of the equilibrium constant A catalyst increases only the rate of the forward reaction A catalyst lowers the activation energy of the reaction 18 Which action will cause an increase in the concentration of PCl 3 in the reaction PCl kj PCl 3 (g) + Cl 2 (g)? adding PCl 5 increasing the pressure by decreasing the volume decreasing the temperature adding argon using a catalyst 19 If k f = 23 x 10-2 s -1 and k r = 68 x 10-2 s -1 for the general equilibrium reaction A B, then what is the value of K c? -45 x x x 10-2

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