Answer. Equilibrium constant is a ratio of the product of concentration of products raised to the power of coefficient to the product of concentration of reactants raised to the power of coefficient as expressed in the balanced chemical equation.
Kc
= Product of concentration of products raised to the power of coefficients
Product of concentration of reactants raised to the power of coefficients
Kc has no units in reactions with equal number of moles on both sides of the equation. This is because concentration units cancel out in the expression for kc, e.g. for the reaction
H2(g) + I2(g) <====> 2HI(g)
Kc = [HI(g)]2 Units (mol dm-3)2
[H2(g) ] [I2(g)] (mol dm-3) (mol dm-3)
For reactions in which the number of moles of reactants and product are not equal in the balanced chemical equation, Kc of course, have units, e.g., for the reaction
N2(g) + 3H2(g) <=====>2NH3(g)
Kc = [NH3(g)]2 = (mol dm-3)2
[H2(g) ] [I2(g)]3 (mol dm-3) (mol dm-3)3
= 1 = mol dm
(mol dm-3)