Just as reflexes vary significantly in speed, so do they vary greatly in extent. Kinetics and equilibrium, in fact, relate to distinct elements of a reaction:

• Kinetics refers to the pace (or speed) of a reaction or the amount of reactant that vanishes (or product that arrives) per unit time.

• Equilibrium refers to the length of a reaction, the concentrations of reactant and product existing after an infinite amount of time, i.e. when no further change occurs.

K is used to quantify the degree of response. At a particular temperature, the magnitude of K indicates how far a reaction progresses toward the product.

Even at the same temperature, different reactions have a broad range of equilibrium concentrations from virtually all reactants to almost all products—and hence a large range of equilibrium constants. Here are three instances of various K magnitudes: K is for little, as shown in the image attached.

If a reaction produces minimal product before reaching equilibrium, the product concentration to reactant concentration ratio is tiny, and the reaction has a small K; if K is very small, we can claim there is "no reaction." At 1000k, there is “no reaction” between nitrogen and oxygen.

• N2(g) + O2(g) ⥫⥬ 2NO(g) K = 1×10−30

The capital letter K, as shown in the image attached. If, on the other hand, a reaction approaches equilibrium with minimal reactant remaining, the product concentration to reactant concentration ratio is big, and it has a large K; if K is really large, we say the reaction "completes." At 1000 K, the oxidation of carbon monoxide “completes”:

• 2CO(g) + O2(g) ⥫⥬ 2CO2(g) K = 2.2×1022

K Intermediate, as shown in the image attached above. When large amounts of both reactant and product are present at equilibrium, K has an intermediate value, such as when bromine monochloride degrades to its constituent components at 1000 K:

• 2BrCl(g) ⥫⥬ Br2(g) + Cl2(g) K = 5

Kinetics and equilibrium are two separate characteristics of a reaction system, and the pace and extent of a reaction are not always connected.

Concentrations no longer exist when the forward and reverse reactions occur at the same rate.

The system has attained equilibrium as a result of the modification. The equilibrium constant (K) is a value based on a certain product/reactant ratio concentrations: If a large concentration of reactant(s) is present at equilibrium, K is small, and if there is a high concentration of product(s) existing at equilibrium, it is big.

The following three criteria define a system at equilibrium:

• 1. Reactant and product concentrations are constant over time.

• 2. The opposing reaction rates are equal: rate fed = rate ref.

• 3. The reaction quotient equals the equilibrium constant: Q = K.

The concentration-based reaction quotient, Qc, is a specific ratio of product to reactant concentrations. As the reaction progresses, the value of Qc changes. Qc = Kc when the system reaches equilibrium at a given temperature.

Because pure liquids and solids have concentration terms equal to one, they do not appear in Q. Because the form of Q is reliant on the balanced equation exactly as stated, it changes if the equation is reversed or multiplied by some factor, and so does K. If a reaction is the result of two or more stages, the overall Q (or K) is the product of the individual Qs (or Ks).

In equilibrium issues, we usually utilize quantities (concentrations or pressures) of reactants and products to determine K, or we employ quantities to find K.

The initial amounts, their changes during the reaction, and the final product are summarized in reaction tables quantities in equilibrium. To make computations easier, we assume that if K is small and the starting amount of reactant equals because the unknown change in the reactant (x) is small, the unknown change in the reactant (y) may be ignored. If this assumption is not supported by evidence, if the resultant inaccuracy is more than 5%, we apply the quadratic formula to calculate x.

We first determine the reaction rate for reactions that begin with a combination of reactants and products. By comparing Q and K, we can determine the direction to decide the sign of x.