Question

A 2.5 L container was initially filled with 0.1 M solution of nitrogen dioxide which decomposes into nitrogen monoxide and oxygen gas according to the following reaction:2NO2(g) ⇌ 2NO(g) + O2(g)After the system has reached equilibrium, the concentration of nitrogen monoxide is found to be 0.05 M. What is the equilibrium concentration of oxygen gas in the container?

Answer 1

To find the equilibrium concentration of oxygen gas, we can use an ICE  Initial, Change, Equilibrium  table to keep track of the changes in concentration for each species involved in the reaction.Initial concentrations:[NO2] = 0.1 M[NO] = 0 M  since the reaction has not yet occurred [O2] = 0 M  since the reaction has not yet occurred Change in concentrations:Since 2 moles of NO2 decompose to form 2 moles of NO and 1 mole of O2, the change in concentration of NO2 is -2x, the change in concentration of NO is +2x, and the change in concentration of O2 is +x.Equilibrium concentrations:[NO2] = 0.1 - 2x[NO] = 0 + 2x = 0.05 M  given in the problem [O2] = 0 + xNow we can solve for x:2x = 0.05 Mx = 0.025 MSo, the equilibrium concentration of oxygen gas [O2] is:[O2] = 0 + x = 0.025 M