A Simple Guide to Calculating Equilibrium Constant

The equilibrium constant of a chemical reaction is the value of the reaction quotient at chemical equilibrium, and if its composition does not show a measurable tendency to change further, then the dynamic chemical system is approaching after sufficient time has passed. Under a given set of reaction conditions, the equilibrium constant is independent of the initial analytical concentration of reactants and product species in the mixture. Therefore, given the initial configuration of the system, known equilibrium constant values can be used to determine the configuration of the system in equilibrium. However, reaction parameters such as temperature, solvent, and ionic strength can all affect the value of the equilibrium constant.

Equilibrium Constant: The equilibrium constant K represents the relationship between the product and reactant of a reaction that is in equilibrium with respect to a particular unit. This article describes how to write the equation for the equilibrium constant and shows the calculations related to both the concentration and partial pressure equilibrium constants.

Types of Equilibrium Constant:

There are two types of equilibrium constant.

• Physical Constant:

When in equilibrium, if the opposite process involves only physical changes, the equilibrium is called physical equilibrium. For example, the equilibrium of water and steam in the evaporation of water. 

 water ⇋ steam

• Chemical Constant

• : When in equilibrium, when the opposite process involves a chemical change, the equilibrium is called chemical equilibrium. For example, balance acetic acid, water, acetate and hydronium ions. The formula is: – 

CH3COOH + H2O ⇌ CH3COO− + H3O +

A Simple Guide to Calculating Equilibrium Constant: There are two things you need to know to calculate the value of the equilibrium constant. The equilibrium equation of the reaction system, including various physical states. From this, an equilibrium equation for calculating Kc or Kp is derived. The various equilibrium concentrations or pressures that appear in the equilibrium equation, or sufficient information to determine them. These values are assigned to the equilibrium equation and the value of the equilibrium constant is calculated. 

• Calculation of K from a known equilibrium set:

       Describe the equilibrium formula of the reaction. 

       Determine the various molar concentrations or partial pressures involved. 

       Substitute in the equilibrium equation and solve K.

• Calculation of K from the initial set and the known equilibrium set:

       Describe the equilibrium formula of the reaction. 

       Determine the various molar concentrations or partial pressures involved. 

       Use the ICE plot to determine the equilibrium concentration or partial pressure. (Whereas “I” stands for the initial concentrations (or pressures) “C” represents the change in the concentrations (or pressures) E” represents the equilibrium concentrations for each species in the reaction mixture.)

       Substitute in the equilibrium equation and solve K 

• Calculate K from known initial quantities and known changes in one quantity of species: 

      Describe the equilibrium formula of the reaction. 

      Determine the various molar concentrations or partial pressures involved. 

      Use the ICE plot to determine the equilibrium concentration or partial pressure. 

      Substitute in the equilibrium equation and solve K.

Equilibrium constant formula:

 K = kf / kb = [C] c [D] d / [A] a [B] b = Kc 

 For reaction with gas: The formula of the equilibrium constant related to partial pressure is as follows. 

K=  kf / kb = [[pC] c [pD] d] / [[pA] a [pB] b] = Kp 

 where Kp is the equation for the equilibrium constant for partial pressure. The larger the 

 Kc / Kp value, the more product formation and the higher the conversion rate. 

 The lower the Kc / Kp value, the less product formation and the lower the conversion rate. 

 Average Kc / Kp values indicate optimal product formation

Units of Equilibrium Constant: The equilibrium constant is the ratio of the increase in concentration to the stoichiometric coefficient. Therefore, the unit of the equilibrium constant = [molL-1] Δn. 

 where ∆n = sum of stoichiometric coefficients of the product – sum of stoichiometric coefficients of the reactants.

CONCLUSION: 

The equilibrium constant of a reaction is calculated from the equilibrium concentration (or pressure) of the reactant and product. If these concentrations are known, the calculation involves simply substituting them into the Kc term. If you know the initial concentration of Kc and the reaction, you can calculate the equilibrium concentration. You can use the ICE plot and the equilibrium constant equation to write equations that explain the changes in the concentration of reactants and products.