How can a chemical equation be used to write a equilibrium-constant expression?

Answer 1

In the equilibrium system:

aA + bB <=> cC + dD

[A]a x [B]b

K = ___________

[C]c x [D]d

Where A, B, C and D are gases or solutions. Pure liquids and solids are not included in the equilibrium constant expression.

Answer 2

Law of mass action (also called 'Law of Guldberg & Waage')
Generalized reaction equation (cf. Note): aA + bB <==> pP + qQ
According to the Law of mass action:
Equilibrium constant (K>/<) is equal to [A(eq)]a.[B(eq)]b / [P(eq)]p.[Q(eq)]q
(only valid for equilibrium concentrations of A(eq), B(eq) and P(eq) and Q(eq) in the one continuous phase, ie. state of matter, the reaction is taking place in)

Note:
A and B are reactant chemical species, P and Q are product species, and a, b and p, q are the stoichiometric coëfficients of the respective reactants and products in the forward (>) and backward (<) balanced reaction equation.

Further reading
On 'Chemical equilibrium, an historical introduction' in wikipedia: look at 'Related links' just below this answer.

Answer 3

Instead of the reaction arrow which looks something like --> it will have the double equilibrium arrow, that looks kind of like an equal sign but with arrowheads on the lines (one arrow pointing each way).

Answer 4

by multiplying the products to the coefficient powers over multiplying the reactants to coefficient powers

Answer 5

chemical equlibrium problems