Question

What does it mean to calculate the average value of the rate constant from the four data sets ? What is average value of the rate constant. What does this mean??
This is about Kinetics in Chemistry.


Also how do I compare the rate of appearance to the rate of disappearance. Do i look at moles ? All of them appear to be gases

Answer 1

1) to calculate average rate from 4 data sets : the order of reaction remain same only reactants concentration and their rate changes

let a simple reaction rate = k [A]^m [B]ⁿ

K1 = rate / [A]^m [B]ⁿ      K2 = rate / [C]^m [D]ⁿ   

K3 = rate / [E]^m [F]ⁿ     K4 = rate / [G]^m [H]ⁿ  

average rate constant = K1+K2+K3+K4 / 4 = K

it means the average of the rate constant of all the 4 data sets

2) it is quite easy to  compare the rate of appearance to the rate of disappearance.

all you have to do is : we take an example so you can better understand

4 NH3 (g) + 5 O2 -------> 4NO + 6H2O

we write rate of reaction

= - 1/4 d[NH3] /dt = -1/5 d[NO2] /dt=1/4 d[NO] /dt = 1/6 d[H2O] /dt

(-ve sign is shows decrease in the concentration of reactant )

1) the rate of reaction is equal to the change in concentration divided by the time interval in which that change occur

2) the rate expression are divided by the stotiometric coefficient that are present in the balanced chemical equation .

we take any two to compare

rate of disappearence of NH3 = rate of formation of NO

1/4 d[NH3] /dt = 1/4 d[NO] /dt

rate of decomposition of  d[NH3] /dt = 4/4 rate of formation of NO

- d[NH3] /dt = 4/4 d[NO] /dt

by this method you can easily compare rate of appearance to the rate of disappearance or vice versa .