Question

In: Chemistry

1) A substance A is consumed by a reaction of unknown order. The initial concentration of...

1) A substance A is consumed by a reaction of unknown order. The initial concentration of A is 1 mM, and concentrations at later times are as shown:

Time (min). [A](mM) 01

  1. 1 0.83

  2. 2 0.73

  3. 3 0.62

5 0.5

10 0.28

15 0.21

a) Test whether a first-order or a second-order reaction best fits the data.


b) What is the rate constant for the reaction?

Solutions

Expert Solution

Rate law for the reaction would be:

R = k[A]n

Where, R is rate of reaction

k is rate constant

n is order of the reaction

we have to calculate the rate of reaction at each concentration given

At 0.83 mM the rate will be equal to (1 - 0.83) / 60 = 0.0028 mM / sec

At 0.73 mM the rate will be equal to (0.83 - 0.73) / 60 = 0.0016 mM / sec

At 0.62 mM the rate will be equal to (0.73 - 0.62) / 60 = 0.00183 mM / sec

At 0.5 mM the rate will be equal to (0.62 - 0.5) / 120 = 0.001 mM / sec

At 0.28 mM the rate will be equal to (0.5 - 0.28) / 300 = 0.00073 mM / sec

At 0.21 mM the rate will be equal to (0.28 - 0.21) / 300 = 0.00023 mM / sec

concentration vs rate
Concentration (mM) Rate (mM/sec)
0.83 0.0028
0.73 0.0016
0.62 0.00183
0.5 0.001
0.28 0.00073
0.21 0.00023

Using excel we can get the equation of data in table above as y = 0.0033(x)1.52

Where, y-axis = rate of reaction

x-aixs = concentration

The equation above is similar to our rate law equation

we can say that the order of reaction = 1.5 and rate constant is 3.3 * 10-3 s-1


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