When a system at equilibrium is disturbed by a change in concentration of one of the components, it reacts in the direction that reduces the change. Example: A(g) + B(g) ⇋ C(l) + D(s) So if the concentration of A is increased the reaction will proceed to use up more A in essence reducing the concentration of B and increasing the concentration of C and D. If the concentration of C is increased, there is no change since C is a liquid and is not part of the equilibrium constant expression. If the concentration of B is reduced the reaction will proceed to make more B and thus make more A as well. If the concentration of D is decreased, there is no change since D is a solid and is not part of the equilibrium constant expression. To improve air quality and obtain a useful product, chemists often remove sulfur from coal and natural gas by treating the contaminant hydrogen sulfide with O2: 2H2S (g) + O2 (g) ⇋ 2S (s) + 2 H2O(g) 1. What happens to the concentration of water if O2 is added? 2. What happens to the concentration of H2S if O2 is added? 3. What happens to the concentration of O2 if H2S is removed? 4. What happens to the concentration of H2S if sulfur is added?
