(Re-post)

Write the equilibrium constant expression, K, for each of the following reactions. Where appropriate, designate the K as Ksp.

2H2(g) + O2(g)<-->2H2O(g)
2Hg(l) + Cl2(g) <-->Hg2Cl2(s)

What's your problem with this? What do you not understand.

well for the first one, should the answer be... K = [H2O]^2

-----------
[H2]^2 + [O2]

or should it just be... K = [H2O]^2?

Your first one is correct except there is no + sign in the denominator. It's supposed to be products over reactants, each raised to the power indicated by the coefficient, so you can't leave out the reactants.

(H2O)^2/(H2)^2(O2)

The second one is
1/(Cl2).
Hg2Cl2 is not included because it's a solid and that's the natural state for it. Hg is not included because that is a liquid and that's the natural state for it. Before you ask about H2O in the first one, H2O(l) would be in the natural state BUT you note that is H2O(g).

To write the equilibrium constant expression for a reaction, we need to write the expression based on the concentrations (for gases) or solubility products (for solids) of the reactants and products.

1. For the reaction: 2H2(g) + O2(g) ⇌ 2H2O(g)

The equilibrium constant expression for this reaction is written as Kc:
Kc = [H2O]^2 / [H2]^2 [O2]

Here, the concentrations in square brackets represent the molar concentrations of each species at equilibrium.

2. For the reaction: 2Hg(l) + Cl2(g) ⇌ Hg2Cl2(s)

Since Hg2Cl2 is a solid, its concentration remains constant throughout the reaction. Therefore, we use the solubility product constant, Ksp.

The equilibrium constant expression for this reaction is written as Ksp:
Ksp = [Hg2Cl2]

Here, the concentration in square brackets represents the solubility product of Hg2Cl2 at equilibrium.

Please note that the equilibrium constant expression can vary depending on the direction of the reaction and the stoichiometric coefficients.