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    Equilibrium and Reactions

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    Question 1
    At 100oC, the equilibrium constant, KC, for the reaction COCl2(g) ?---? CO(g) + Cl2(g) has a value of 2.19 x 10-10. Is the following mixture at equilibrium? If not, indicate the direction in which the reaction must proceed to achieve equilibrium.
    [COCl2] = 5.00 x 10-2 M, [CO] = [Cl2] = 3.31 x 10-6 M

    Question 2
    Consider the following equilibrium:
    2 SO2(g) + O2(g)?----? 2 SO3(g), ?H = -198.2 kJ
    Choose the TRUE statement(s) from among the following:
    i) The equilibrium constant expression is KC = [SO3]2/[SO2]2[O2].
    ii) Reducing the volume of the container would shift the equilibrium to the right.
    iii) Adding more O2 would shift the equilibrium to the right.
    iv) Raising the temperature would shift the equilibrium to the right.
    v) Changing the temperature would affect the magnitude of the equilibrium constant.

    Question 3
    For which of the following systems at equilibrium will shift to produce more products when the volume of the container is decreased?
    i) H2(g) + I2(g) ?----? 2 HI(g)
    ii) 2 NO2(g) ?----? N2O4(g)
    iii) PCl5(g) ?----? PCl3(g) + Cl2(g)
    iv) ZnO(s) + CO2(g) ?----? ZnCO3(s)

    Question 4
    The equilibrium constant Kp = 0.90 for the following reaction in the gas phase:
    H2O(g) + Cl2O(g) ?----? 2HOCl(g).
    Calculate the equilibrium pressure of HOCl in the reaction vessel if the initial pressures of H2O and Cl2O are both 0.50 atm.

    Question 5
    A 10.0 gram sample of solid PCl5 was placed in a 1.00 litre vessel and heated to 250 oC. All components are in the gas phase at this temperature. Kp = 0.70 at 250 oC. Calculate the total pressure in the reaction vessel at equilibrium.
    PCl5(g) ?----?PCl3(g) + Cl2(g).

    Question 6
    Solid silicon reacts with chlorine gas to form gaseous SiCl4 at elevated temperatures. When the reaction is started with 0.10 mol Si and 0.20 mol Cl2 in a one-liter flask, 0.050 mol SiCl4 are obtained. The equilibrium constant, KC is:

    Question 7
    Consider the following reaction in the gas phase: H2 + I2 ?----?2 HI. At some temperature, the equilibrium constant (Kc) is 4.0. The reaction is started with equimolar quantities of H2 and I2. When equilibrium is established, 0.20 mol HI is present. How much H2 was used to start the reaction?

    Question 8
    What is the relationship of the equilibrium constants for the following two reactions?
    (1) 2NO2(g) ?----?N2O4(g)
    (2) N2O4(g) ?----?2NO2(g)

    Question 9
    A catalyst serves to:

    a. ) shift the equilibrium to the left.
    b. ) shift the equilibrium to the right.
    c. ) shift the equilibrium to the right or the left depending on the reaction.
    d. ) speed up a reaction.
    e. ) slow down a reaction.

    Question 10
    The equilibrium constant, Kp , has a value of 6.5 × 10-4 at 308 K for the reaction of chlorine with nitric oxide.
    2NO(g) + Cl2(g) ?----? 2NOCl(g)
    What is the value of Kc?

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    Solution Preview

    1. The answer is (a) because

    Kc = [Cl2][CO]/COCl2] = [(3.31x10^-5)^-2]/(5.00x10^-2) = 2.19x10^-10

    2. The answer is (d). The only false statement above is (iv).

    3. The answer is (c). Reactions (ii) and (iv) will have a shift to the right producing more product when the volume is decreased.

    4. The equilibrium expression for the reaction above is

    Kp = (P_HOCl)^2 / (P_H20)(P_Cl2O) = 0.90

    We ...

    Solution Summary

    This solution contains calculations and explanation as well as correct answers for each multiple choice question.