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

Answer 1

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 2

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 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

A chemical equation can be used to write an equilibrium constant expression by taking the concentrations of products raised to their stoichiometric coefficients and dividing by the concentrations of reactants raised to their stoichiometric coefficients. The equilibrium constant expression is written in terms of the molar concentrations of the species involved in the reaction.

Answer 5

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

Answer 6

chemical equlibrium problems