Equilibrium Constant and Its Significance: Embibe Exams
  • Written By trisha
  • Last Modified 21-07-2022
  • Written By trisha
  • Last Modified 21-07-2022

Equilibrium Constants and its Significance

Equilibrium Constants: In chemistry, equilibrium is achieved when the rate of forward reaction equals to the rate of backward reaction. The equilibrium constant of a chemical reaction is defined as the value of the reaction quotient under conditions of chemical equilibrium. It is also referred to as the state by which dynamic equilibrium can be achieved after sufficient time has ended. The composition is having no measurable tendency toward any type of further changes.

Chemical Equilibrium Constant
Chemical Equilibrum

Under a given set of reaction conditions, the equilibrium constants are independent of the initial analytical concentrations of the reactants and the products which are present in the mixture. The initial composition of the system is known by the name of the equilibrium constant. The values are used for the determination of the system equivalent composition.

Know More About Equilibrium Constant

Formula of Equilibrium Constant

The equilibrium constant is usually denoted as Kc. The unit of the equilibrium constant is [Mole L-1]△n.

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

Keq = kf/kb = [C]c [D]d/[A]a [B]= Kc

Kc is measured in moles per litre.

For reactions involving gases: The equilibrium constant formula, in terms of partial pressure will be:

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

Where Kp indicates the equilibrium constant formula in terms of partial pressures.

  • Larger Kc/Kvalues indicate higher product formation and higher percentage conversion.
  • Lower Kc/Kp values indicate lower product formation and lower percentage conversion.
  • Medium Kc/Kp values indicate optimum product formation.

Factors Affecting Equilibrium Constants

The following factors are known to influence the Kc of a reaction:

  • The temperature of the mixture- With an increase in the temperature of the solution medium, the value of the equilibrium constant decreases. This happens when the forward reaction is endothermic, and the temperature value increases for Kc. The position of equilibrium also changes if you change the temperature.
  • Solvent of the mixture- Solvent polarity with cis-enol form is the main dominating form where the equilibrium constant gets valued. The intramolecular H-bond formed in the cis-enol form is more pronounced when there is no competition for intermolecular H-bonding with the solvent.
  • Ionic Strength- With the increasing ionic strength of a solution, the activity coefficient decreases.

Significance of Kc

The following points are given below that highlight the importance of equilibrium constant in the language of chemistry:

Predicting the extent of the reaction: The equilibrium constant (Kc) is used for predicting the extent of the chemical reaction. In other words, it dictates the degree of the disappearance of the reactants.

For example,
N2 (g) + O2 (g) ⇌ 2NO (g) ⇒ Kc =4.8 × 10-31 at 298K
H2O (g) ⇌ H2 (g) + (1/2) O2 (g) ⇒ Kc = 4.1 × 10-48

Predicting the direction of the reaction: Reaction quoteint, Qc is used for predicting the direction of a chemical reaction. It helps in knowing whether will progress in a forward direction or regress in a backward direction.

For a balanced reaction, aA + bB ⇌ cC + dD
Reaction quotient (Qc or Qp) is given as:

Qc = [C]c[D]d/[A]a[B]b
Qp = pcC × pdD / paA × pbB

Equilibrium Constant and Its Significance

Comparison with Kc and the direction of Reaction:

  • If Q = Kc, the reaction is in equilibrium [Where, Kc = equilibrium constant]
  • If Q > Kc, Q will tend to decrease so as to become equal to K. As a result, the reaction will proceed in the backward direction.
  • If Q < Kc, Q will tend to increase so as to become equal to K. As a result, the reaction will proceed in the forward direction.

Chemistry related articles

Thermodynamic ProcessesHomogeneous Equilibria
Glucose Chemical ProcessHeterogeneous Equilibria

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