The equilibrium constant, k c, for the reaction n2o4 (g) ⇄ 2no2 (g) is 0.211 at 100°c. if the equilibrium concentration of n2o4 is 0.00251 m, calculate the equilibrium concentration of no2.

Answer is: 0.0213M.
Reaction: N₂O₄ (g) ↔ 2NO₂ (g).
Kc = 0,211 at 100°C.
Kc - equilibrium constant.
c (N₂O₄) = [N₂O₄]  = 0,00251M.
c (NO₂) = [NO₂] = ?
Kc = [NO₂]² / [N₂O₄] 
[NO₂]² = Kc · [N₂O₄]
[NO₂] = √(Kc · [N₂O₄]) 
[NO₂] = √(0.211 · 0.00215M) 
[NO₂] = 0.0213M.

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