Equilibrium expression for formation of nitrosyl bromide 2NO + Br2 2NOBr

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: 2NO + Br2 <------> 2NOBr, it can be seen that the equation
is balanced. As NO, Br2 and NOBr are gases; the equilibrium expression is in terms of
their partial pressures.

Kp =
P(NOBr)^2/P(NO)^2 * P(Br2), 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.