Inorganic and Applied Chemistry

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Inorganic and Applied Chemistry

Example 3- C:

Decomposition of nitrogen dioxid

In an experiment we begin by having a flask of gas filled with NO 2 at room temperature (25 ºC). At this

temperature NO 2 is stabile, but if the gas is heated up to 300 ºC, it decompose to NO and O 2 following the

following reaction scheme:

2 NO 2 (g)  2 NO(g) + O 2 (g)

By measurement of the concentration of the three gases as function of time, the following data is obtained:

Time in

seconds

Concentration of NO 2 Concentration of NO Concentration of O 2

0 0,01 0 0

50 0,0079 0,0021 0,0011

100 0,0065 0,0035 0,0018

150 0,0055 0,0045 0,0023

200 0,0048 0,0052 0,0026

250 0,0043 0,0057 0,0029

300 0,0038 0,0062 0,0031

350 0,0034 0,0066 0,0033

400 0,0031 0,0069 0,0035

By applying equation (3-1) it becomes possible to determine the velocity, by which O 2 is formed. For

instance is O 2 formed in the time interval 150 s  200 s with the velocity:

 

 L s

mol

s s

mol L mol L

t

A



^6

(^2) ( 200 150 )^6.^010
Rateofreaction(formationofO ) (^0 ,^0029 /^0 ,^0026 / )
while the velocity in the interval 350 s  400 s is:

 L s
mol
s s
mol L mol L
t
A

^6
(^2) ( 400 350 )^4.^010
Rateofreaction(formationofO) (^0 ,^0035 /^0 ,^0033 / )
It is thereby worth noting that the rate of reaction is not a constant factor but actually decreases with time
in this case.
Reactions kinetics