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Chemistry 213 Sample Test 2 WINONA STATE UNIVERSITY

Dr. Myoung Lee

Name:______

Show your work for full credits and follow the rules of significant figures in your calculation.

Summary of Kinetics for Reactions

Order

Zero / First / Second

Rate law

/ Rate = k / Rate = k[A] / Rate = k[A]2
Integrated rate law / [A] = -kt + [A]o / ln[A] = -kt + ln[A] o / 1/[A] = kt + 1/[A] o
Half-life (t 1/2) / [A] o /2k / 0.693/k / 1/k[A] o

Arrhenius equation

k = Ae-Ea/RT

lnk = - (Ea/R) (1/T) + lnA

R = 8.314 J/mol.K

1.  The following data were obtained for the reaction:

2ClO2(aq) + 2OH-(aq) -> ClO3- (aq) + ClO2-(aq) + H2O(l)

[ClO2] (M) / [OH-] (M) / Initial Rate (M/s)
0.0100 / 0.200 / 0.0254
0.0200 / 0.200 / 0.1020
0.0200 / 0.100 / 0.0507

a.  Determine the rate law.

b.  Determine the value of the rate constant.

c.  What concentrations of ClO2 and OH- can you use to achieve an initial rate of 0.406 M/s? You may have more than one correct answer.

2.  A certain radioactive decay process follows a first-order rate law. This process is 40.0% complete in 30.0 minutes. Determine the rate constant and the half-life for this process.

3.  Draw a sketch of the energy profile for a two-step mechanism where the first step is rate-determining. The overall energy change is exothermic. Indicate each of the following on the profile.

a.  The position of reactants.

b.  The position of products.

c.  The position of intermediates.

d.  The activation energies for the first step.

e.  The activation energies for the second step.

f.  The overall energy change.

4.  Evaluate each of the following statements. Do you agree or disagree with the statement? Explain your reasoning.

a.  Reactions with large rate constants also have large equilibrium constants.

b.  When a system reaches an equilibrium, the value of the reaction quotient, Q, equals that of the equilibrium constant, K.

c.  At equilibrium, the rate of the forward reaction equals the rate of the reverse reaction.

d.  A catalyst increases the rate of a chemical reaction by decreasing the activation energy.

e.  The concentration of a homogeneous catalyst decreases as a reaction proceeds.

f.  The conjugate base of a weak acid is relatively stronger than the conjugate base of a strong acid.

g.  The end point of a titration is identical to the equivalence point of a titration.

h.  A certain reaction has a higher equilibrium constant at a lower temperature. It indicates that this reaction is exothermic.

i.  In deciding which of two acids is the stronger, one must know the acid dissociation constant (Ka) of each acid.

5.  Sketch the titration curve for the titration of a generic weak acid with a strong base. On the curve, indicate the following points:

a.  pH = pKa of the weak acid

b.  The region with maximum buffering

c.  The equivalence point

6.  Calculate the hydrogen ion concentration and the pH of each of the following solutions.

a.  0.200 M acetic acid, HC2H3O2 (Ka = 1.8 x 10-5)

b.  0.200 M acetic acid, HC2H3O2, and 0.750 M sodium acetate, NaC2H3O2

c.  0.200 M NaOH

d.  0.200 M HNO3

e.  0.200 M HF and 0.500 M NaF (Ka = 7.2 x 10-4)