What is the equilibrium expression for this equation 2HFH2+F2

The equilibrium expression for any chemical reaction can
be determined if the phase of each substance that constitutes the chemical equation is
known and the equation is balanced with the same number of atoms of each element on both
the sides.

The equilibrium expression can be in terms of
the concentration of each substance that makes up the equation or if there are gases
involved it can be terms of the partial pressure.

For the
equation given: 2HF<------->H2 + F2, the reactants as well as products are
gases.

2HF(g)<------->H2(g) +
F2(g)

The equation is balanced with two molecules of
hydrogen fluoride at equilibrium with one molecule of hydrogen and one molecule of
fluorine. The equilibrium expression is written in terms of the partial pressures of all
the constituent compounds.

Kp =
P(H2)*P(F2)/P(HF)^2, where P(X) is the partial pressure of X and it is
raised to the power equal to the number of molecules in the balanced chemical
equation.