Ans_Ex6 - Nielsen CHM1041 Answer to Exercise Set 6 General Equilibria 1 Why is a chemical equilibrium referred to as a dynamic equilibrium A

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Nielsen Bhaskar/PC/1713-I/A 2/05 1 CHM1041 Answer to Exercise Set # 6 General Equilibria 1. Why is a chemical equilibrium referred to as a dynamic equilibrium? A chemical equilibrium is established when the rate of the forward reaction is equal to the rate of the reverse reaction, and there is no net change in the relative quantity of the reactants to products. The equilibrium is described as “dynamic” and not “static” since neither the forward nor reverse process has stopped. “Dynamic” indicates motion, a characteristic of equilibrium that needs emphasis. 2. Write the expressions for the equilibrium constant K for the following equilibria: a) 22 N + 0 2 N0 ZZX YZZ [ ] [] 0 0 N K N = b) 2S 3 0 + 0 2 S0 [ ] 2 3 2 0 00 S K S = c) S 8 8 S [ ] 8 r S K S = d) CH 42 + 2H S CS + 4H [ ][ ] 4 2 CS H K CH H S = e) 4NH 32 + 50 4 NO + 6 H 0 [ ] [ ] [ ] 46 2 45 0 0 NO H K NH =
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Nielsen Bhaskar/PC/1713-I/A 2/05 2 3. The equilibrium constants for four different reactions are 1.3 x 10 1 , 2.6 x 10 -21 , 4.7 x 10 -2 , and 1.8 x 10 12 . Assuming that each reaction can be represented in the form A + B ZZX YZZ C + D, which of the four systems represents an equilibrium mixture essentially composed of just two substances? For the equilibrium expression, [ ][ ] [] CD = K AB , an equilibrium that resulted in equal concentrations of all reactants and products would yield K = 1. A value of K greater than one would indicate a greater proportion of products at equilibrium; a value of K less than one would indicate a greater proportion of reactants. Comparing the four possible values of K, i.e. , 1.3 x 10 1 , 2.6 x 10 -27 , 4.7 x 10 -2 , and 1.8 x 10 12 , the values of 1.3 x 10 1 and 4.7 x 10 -2 are reasonably close to 1 to indicate a significant concentration of all reactants and products at equilibrium. The value of K of 2.6 x 10 -27 requires the product of [A] [B] to be extremely large compared to the product of [C] [D]. The concentrations of C and D would be so small that for practical considerations no reaction could be assumed, i.e. , only A and B would be present. The value of K of 1.8 x 10 12 requires the product of [C] [D] to be very large compared to the product of [A] [B] and the reaction may be assumed to go to completion, i.e. , the reverse reaction would be of relatively minor concern. 4. A mixture of 0.0080 mole of S0 2 (g) and 0.0056 mole of 0 2 (g) is placed in a one-liter container at 1000°K. When equilibrium is established, 0 S 2 (g) and 0.0056 mole of 0 2 (g) is placed in a one-liter container at 1000ºK. When equilibrium is established, 0.0040 mole of S0 3 (g) is present. 2 S0 2 (g) + 0 2 (g) Z ZX 2 S0 3 (g) a) What are the equilibrium concentrations of S0 2 (g) and 0 2 (g) ? 2 S0 2 (g) + 0 2 (g) 2 S0 3 (g) Start 0.0080 0.0056 0 Equilibrium (0.0080-0.0040) (0.0056-0.0020) (0.0040) Moles in one liter container 0.0040 mole A 0.0036 mole A 0.0040 mole A b) What is the value of K for the equilibrium at 1000ºK? [ ] [ ] [ ] 2 3 2 22 0 0.0040 2.8 10 0 0 0.0040 0.0036 S Kx S == = 5. Into a 5.00 liter flask was placed a 35.7 g PC1 5 . The flask and contents were heated to 250ºC and then held at that temperature until the following equilibrium was established: PC1 5 (g) PC1 3 (g) + C1 2 (g)
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Nielsen Bhaskar/PC/1713-I/A 2/05 3 It was then shown by analysis that 8.75 g of C1 2 was present in the equilibrium mixture.
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This note was uploaded on 12/12/2011 for the course CHM 2041 taught by Professor Staff during the Fall '09 term at Santa Fe College.

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Ans_Ex6 - Nielsen CHM1041 Answer to Exercise Set 6 General Equilibria 1 Why is a chemical equilibrium referred to as a dynamic equilibrium A

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