How to write solubility equilibrium and solubility-product constant expression?

Equilibrium stuff.?

• Write an expression for the ionic product of water Kw Write an expression for Kp in the following: 2NO2 -> N2O4 Write an expression for the equilibrium constant of the following reaction: NO(g) + Br2(g) <--> NOBr(g). What exactly is it asking for when it says, "write an expression," and how do I do it?

• Answer:

  In general, the expression for an equilibrium constant expression is in the form: k = [products]/[reactants] eg for 2NO2 -> N2O4 kc = [N2O4]/[2NO2]^2 (NB the concentration of NO2 is squared because there are two of them.) for NO(g) + Br2(g) <--> NOBr(g) k c= [NOBr]/[NO] [Br2] As the above are gas reactions, you could also write kp = pNOBr/pNO.pBr2 For the ionic product of water, kw you start with the equation for the self ionisation of water ie H2O ---> H^+ + OH^- I trust that you can go from there. I hope the above helps.