(a) Determine the order of the reaction with respect to S2O82-, with respect to
ID: 484230 • Letter: #
Question
(a) Determine the order of the reaction with respect to S2O82-, with respect to I-, and the overall.
(b) What is the value of the rate of constant k?
(c)What would be the initial rate of reaction if [S2O82-] = 0.083 M and [I-] = 0.115 M ?
462. The rate of the following reaction in aqueous solution is monitored by measuring the rate of formation of I3 Data obtained are listed in the table. SnO, 3 SO. Experiment run initial rate Ms 1.4 x 105 0.038 0.060 2.8 x 105 0.076 0.060 3 5.6 x 105 0.120 0.076Explanation / Answer
In order to calculate the rate law expression for a A+B reaction, we need to apply Initial Rates Method.
Note that the generic formula goes as follows:
r = k [A]^a [B]^b
Note that if we got at least 3 sets of point, in which we have A and B constant, then we could use:
r1 / r2 = (k1 [A]1^a [B]1^b) / (k2 [A]2^a [B]2^b)
If we assume K1 and K2 are constant, then K1= K2 cancel each other
r1 / r2 = ([A]1^a [B]1^b) / ( [A]2^a [B]2^b)
Then, order according to [A] and [B]
r1 / r2 = ([A]1/[A2])^a * ([B]1/[B]2)^b
If we get two points in which A1 = A2, then we could get B, and vise versa for A...
From the data shown in YOUR table
Choose point 2 and 3...
r2 / r3 = ([A]2/[A3])^a * ([B]2/[B]3)^b
substitute
(2.8*10^-5) / (5.6*10^-5) = (0.076/0.076)^a * (0.06/0.12)^b
Cleary, the coefficient cancels:
0.50= 1 * (0.5)^b
solve,
ln(0.50) / ln(0.5) = b
b = 1
Choose now points 1 and2:
r1 / r2 = ([A]1/[A]2)^a * ([B]1/[B]2)^b
substitute
(1.4*10^-5)/(2.8*10^-5) = (0.038/0.076)^a * (0.06/0.06)^b
Cleary, the coefficient cancels:
0.5= (0.5)^a * 1
solve,
a = 1
so...
a = 1, b = 1
then
r = k [A]^a [B]^b
so
r = k [A]^1 [B]^1
For "k" value... choose any point in your set of data, I will choose 1 for simplicity
substitute data
r = k*[A]*[B]
1.4*10^-5= k*(0.038)(0.06)
K = (1.4*10^-5)/((0.038)(0.06)) = 0.0061403 1/(M^-1 s^-1)
c)
Rate:
r = k [A]^1 [B]^1
r = 0.0061403 *(0.083)(0.115) = 0.0000586= 5.86*10^-5 M/s
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