A certain amount of nitrogen dioxide gas (NO2
) in a closed container whose volume can be
varied. The container, with initial volume of 100 cm3
, is left for a while so the following reaction
takes place until an equilibrium is reached:
2NO2
(g) ⇌ N2
O4
(g) ΔH < 0
At equilibrium it is found that the NO2
concentration is 0,4 mol∙dm–3 . The equilibrium constant,
Kc
, at this temperature is 2.
3.1 Calculate the initial amount (in mol) of NO2
(g) that was sealed in the container.
To solve this problem, we can use the equilibrium expression and the given concentration of NO2 to calculate the initial amount (in moles) of NO2.
The equilibrium expression for the given reaction is:
Kc = [N2O4] / [NO2]^2
We are given that Kc = 2 and [NO2] = 0.4 mol/dm³. We need to find the initial amount of NO2, which we can represent as x mol.
Plugging in the given values into the equilibrium expression, we have:
2 = [N2O4] / (0.4)^2
Rearranging the equation, we have:
[N2O4] = 2 * (0.4)^2
[N2O4] = 0.32 mol/dm³
The volume of the container is initially 100 cm³, which is equivalent to 0.1 dm³. Therefore, the initial amount of NO2 can be calculated by multiplying the concentration of NO2 by the volume of the container:
Initial amount of NO2 = [NO2] * volume
= 0.4 mol/dm³ * 0.1 dm³
= 0.04 mol
Thus, the initial amount of NO2 that was sealed in the container is 0.04 mol.