The reaction I^- + OCl^- OI^- + Cl^- was studied in basic aqueous media. The dat

Question

The reaction I^- + OCl^- OI^- + Cl^- was studied in basic aqueous media. The data below was collected at 25 degree C. (None of the solutions initially contained OI^- or Cl^-.) a) The rate law can be expressed as R = k[I^-]^a[OCl^-]^b[OH^-]^c. Enter the values of a, b, and c in that order, to two significant figures. b) Enter the value of k to two significant figures and no units. Next, enter the letter without the semicolon corresponding to the right units (a; s^-1; b: M^-1 s^-1; c: M^-2s^-1; d: M^-3 s^-1; e: M^-1 s^-2). c) Is the rate law consistent with the following mechanism? d) Increasing the temperature to 125 degree C increases the rate constant by a factor of 160. What is the activation energy in kJ/mol? Use two significant figures and do not enter the units.

Explanation / Answer

1) In first and second experiment, the concentration of ICl- and OH- is kept constant while concentration of I- is doubled. The rate also increases two fold. So, this reaction is first order with respect to concentration of I-.

a = 1.0

In second and fourth experiment concentration of I- and OH- is kept constant while concentration of OCl- is doubled. the rate of the reaction is also doubled. So, the reaction is first order with respect to concentration of OCl^-.

b = 1.0

Consider reaction 2 and 3. Here concentration of I- is decreased by half and concentration of OCl^- is increased by two. As both of them are first order, the will cancel each other.So, the reaction rate will depend on increase in concentration of OH-.As observed, the rate is decreased 1/2 fold. So, the reaction is -1.0th order with respect to OH- concentration .

c = -1.0

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k = rate/[I-][OCl-][OH-]^-1

   = 1.8 *10^-4/ (2*10^-3)(1.5*10^-3)(1.0)^-1

   = 60 M^-2 S^-1

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the rate law is not consistant with the mechanism

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ln (k2/k1) = Ea/R [1/T1-1/T2}

or, ln (160) = Ea/8.314 J/K/mol [1/298 - 1/398]

or, Ea = 50.045 kJ/mol

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