What is the Keq of Cl2(aq) + 2HI2(g) -> I2(s) + 2HCl(s)

Solid is not included in the Keq expression, so what would Keq be?

Thanks in advance.

I wonder if HCl is a solid or (aq). I don't know what HI2 is; I suspect that is a typo and should be 2HI. That equation isn't balanced as is. If as shown, then

Kc = 1/(Cl2)(HI)^2

There are 3 mols on each side. I made the question up, so I think HCl was supposed to be a gas.

I was just wondering if it would be Keq = 0/(Cl2)(HI)^2 or Keq= 1/(Cl2)(HI)^2. Thanks for clearing it up.

No, Keq can't be zero on top. By definition, the activity of a solid is 1; therefore, 1 goes on top.

For the balancing, you do not balance total moles to equal total moles. You DO balance moles (or atoms) of individual elements. So a balanced equation could be
Cl2(aq) + 2HI(g) ==>I2(s) + 2HCl(s)

Whoops, forgot the rules to balancing an equation for a second, thanks! :)

Is the activity of pure liquids, 1, as well?

Yes, the activity of a pure liquid is 1. The activity of a pure solid is 1.

To determine the Keq for the given reaction, we need to write the balanced equation and understand the correct way to express it in terms of concentrations.

The balanced equation is:
Cl2(aq) + 2HI2(g) → I2(s) + 2HCl(s)

Keep in mind that Keq is an expression of the equilibrium constant and relates the concentrations (or partial pressures, depending on the reaction) of the products to the concentrations (or partial pressures) of the reactants at equilibrium.

In this equation, the solid (s) state does not affect the concentration terms, so it is not included in the expression for Keq. Therefore, we only need to consider the aqueous (aq) and gaseous (g) species.

The correct way to express the Keq would be:
Keq = [HCl]^2 / [HI]^2

Here, [HCl] represents the concentration of HCl, and [HI] represents the concentration of HI. The exponents are based on the stoichiometry of the balanced equation.

By plugging in the equilibrium concentrations of HCl and HI once the reaction has reached equilibrium, you can solve for Keq using the given concentrations.