My best answer would be:

Question

HCl]4[O2] / [H2O]2[Cl2]2

Is this correct?

Answer 1

for what problem?

Answer 2

Taking note of the equilibrium

4HCl(g) + O2(g) ----> 2H2(g) + 2Cl2(g).

What would be the the equilibrium law expression for the balanced chemical equation?

Answer 3

No. It's the product of the PRODUCTS of the reaction divided by the product of the REACTANTS, each raised to a power indicated by its coefficients in the balanced equation.

Answer 4

I want to apoligize. The equilibrium is

4HCl(g) + O2(g)--->2H2O(g) + 2Cl2(g)

Not

4HCl(g) + O2(g) ---> 2H2(g) + 2Cl2(g).

Answer 5

And the equilibrium STILL is the product of the products of the reactants, divided by the product of the reactants, each raised to a power indicated by the coefficient in the balanced chemical equation. The products of the reaction are H2O and Cl2 in your corrected equation. The reactants are HCl and O2.