What is the relationship between reaction rate and molecular equillibrium?

Reaction rate tells us how fast or how slow a reaction proceeds. There are certain reactions that are reversible. This means that the reactant can form products and the products can form back the reactants. The reaction will proceed until it reaches equilibrium. Equilibrium is achieved when the rate of the forward reaction is equal to the rate of the reverse reaction. In equation form:
Sample reaction
R1 + R2 <--> P1 + P2

rate(forward) = rate(reverse)
kf [R1][R2]=kr [P1][P2]
K = kf/kr = [P1][P2]/[R1][R2]

K is the equilibrium constant
kf is the rate constant of the forward reaction
kr is the rate constant for the reverse reaction

[R1], [R2], [P1], [P2] = concentration of reactants (R) and products (R) (examples)