[Jess!ca]

Here's the q:

N2O4 and NO2 coexist in this equilibrium..

2 NO2 <--=--> N2O4

A chemist adds 4.00mol no2 to a container with a volume of 2dm3. The container is sealed, heated to a constant temp and allowed to reach equilibrium.

the equilibrium mixture contains 3.2mol no2. Calculate Kc under these conditions.

I understand everything up to the point where reacting ratio is 2:1 and that concentration of no2 is 1.6mol dm3. So I thought that the conc. of N2O4 would be 0.8, but markscheme says its 0.2. Why is this??

[EierVonSatan]

0.8 mol of NO₂ has reacted, which means 0.4 mol of N₂O₄ is present according to the ratio in the chemical equation. Convert moles into concentration and it should be obvious