In: Chemistry
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 0.83
2 0.73
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?
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 (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