equilibrium stuff.?

Question

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 1

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.

Answer 2

Kp = p(N2O4) / p(NO2)^2
where p = partial pressure

Kc = [N2O4]/[NO2]^2

Kw of water = [H+][OH-]
pKw = -log10 Kw