Question

Concentration time data were collected for the following reaction at 30 oC

A + B --> 2C
Concentration time data at T = 30oC
Time (s) [A] (mol L-1)
0 0.65
15 0.52
30 0.35
45 0.28
60 0.22
75 0.14
90 0.095


(i) Calculate the average rate of consumption of A in the first 15 seconds of reaction.
(ii) Calculate the average rate of production of C in the first 15 seconds of reaction.
(iii) Calculate the average rate of consumption of A in the last 15 seconds of the reaction.
(iv) Explain the difference between the rates of consumption calculated in (i) and that in (iii)

Answer 1

(i) Calculate the average rate of consumption of A in the first 15 seconds of reaction: -8.67X10^(-3) M/s

(ii) Calculate the average rate of production of C in the first 15 seconds of reaction: 0.0.17 M/s

(iii) Calculate the average rate of consumption of A in the last 15 seconds of the reaction: -3x10^(-3) M/s

(iv) Explain the difference between the rates of consumption calculated in (i) and that in (iii): At the beginning the reaction, is fast, then, when time passes, the reaction slows because there are less concentration of the reactants to produce C, so the rate is less.

Step-by-step explanation:

The general formula to calculate any reaction rate is:

`r=(\Delta [Concentration])/(\Delta t)`

With this formula we can make the calculations, and we can know if r is positive or negative by knowing if we are calculating for a reactant or a product, positive for products, negative for reactants.

(i)

`r=(0.52-0.65)/(15)=-8.67x10^(-3) M/s`

(ii)

In this case we need to multiply delta by 2, because 1 mole of A produces 2 moles of C:

`r=2*(0.52-0.65)/(15)=-0.017M/s`

As we know it is a product, r needs to be positive, so we change the sign of the result and we have: 0.017 M/s

(iii)

`r=(0.095-0.14)/(15)=-3x10^(-3) M/s`

(iv)

Is already answered in the upper part.