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PS6_Key

# PS6_Key - Chemistry 2080 Spring 2009 Problem Set#6 due date...

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Chemistry 2080 Spring 2009 Problem Set #6 - due date: Friday, March 13th at 2 pm Name:__ _KEY__________ Lab TA Name:__________________ Lab Day/Time:______________________ Practice problems (not graded). Chapter 16: 17, 19, 25, 27, 41, 44 1) The pK a for acetic acid (CH 3 CO 2 H) is 4.74 at 25°C. The pK a for the conjugate acid of the weak base ammonia is 9.25 at 25°C. a) Calculate the value of the equilibrium constant K c for the following aqueous equilibrium: CH 3 CO 2 H(aq) + NH 3 (aq) CH 3 CO 2 (aq) + NH 4 + (aq) Let’s call CH 3 CO 2 H(aq) = AcOH and CH 3 CO 2 (aq) = AcO K a 1 = [AcO ][H 3 O + ] [AcOH] = 10 4.74 = 1.82 × 10 5 K a 2 = [NH 3 ][H 3 O + ] [NH 4 + ] = 10 9.25 = 5.62 × 10 10 we want the equilibrium: [AcO ][NH 4 + ] [AcOH][NH 3 ] = K a 1 K a 2 = 1.82 × 10 5 5.62 × 10 10 and this equals 3.2 x 10 4 b) Remember that at equilibrium, the rates of the forward reaction and the back (reverse) reaction are equal. Express the equilibrium constant K c for the above equilibrium in terms of the forward and the reverse rate constants, k f and k r respectively. K c = k f k r c) The rate constant for the forward reaction (k f

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PS6_Key - Chemistry 2080 Spring 2009 Problem Set#6 due date...

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