Equilibrium Constant Expression Calculator Online

The equilibrium constant expression calculator is designed to compute the equilibrium constant (K) for a given chemical reaction. This constant is a fundamental parameter in chemical thermodynamics, representing the ratio of the concentration of products to reactants at equilibrium. Knowing the value of K helps predict the extent and direction of chemical reactions.

Formula of Equilibrium Constant Expression Calculator

The calculation of an equilibrium constant involves several steps, each based on fundamental chemical principles:

Balanced Chemical Equation

Every calculation must start with a balanced chemical equation. This equation ensures that the number of atoms for each element is the same on both sides of the reaction, adhering to the law of conservation of mass.

Concentrations or Pressures

Depending on the nature of the reaction, the equilibrium constant can be expressed in terms of concentrations (Kc) or partial pressures (Kp). Concentrations are used for reactions occurring in solutions, while pressures are used for gaseous reactions, each denoted by square brackets [].

Stoichiometric Coefficients

The coefficients in the balanced equation indicate the number of moles of each reactant and product involved. These coefficients are used as exponents in the expression, directly influencing the calculation of K.

Products over Reactants

The equilibrium expression is formed by dividing the product of the concentrations of the products, each raised to the power of its stoichiometric coefficient, by the product of the concentrations of the reactants, similarly raised.

For example, for the reaction aA + bB <=> cC + dD, the equilibrium constant expression is:

K = [C]^c * [D]^d / [A]^a * [B]^b

Table of General Terms and Calculator Utility

Term	Definition	Utility in Calculations
Reactants	Substances consumed in a chemical reaction.	Enter their concentrations or pressures in the formula.
Products	Substances formed in a chemical reaction.	Enter their concentrations or pressures in the formula.
Stoichiometric Coefficient	Number indicating the ratio of reactants to products in a balanced equation.	Used as exponents in the equilibrium constant expression.
Equilibrium Concentration	Concentration of reactants or products in a mixture at equilibrium.	Directly used in calculating the equilibrium constant.
Partial Pressure	Pressure exerted by a single gas in a mixture of gases.	Used for KpKp​ calculations in gaseous reactions.
Kc​ (Equilibrium Constant for Concentrations)	Ratio of product concentrations to reactant concentrations at equilibrium.	Used for reactions in solution.
Kp​ (Equilibrium Constant for Pressure)	Ratio of product pressures to reactant pressures at equilibrium.	Used for gaseous reactions.

Example of Equilibrium Constant Expression Calculator

To illustrate how the equilibrium constant expression calculator works, let’s go through a detailed example using the reaction between nitrogen (N2) and hydrogen (H2) to form ammonia (NH3):

Balanced Chemical Equation: N2 + 3H2 <=> 2NH3

1. Identify the Reactants and Products: Here, nitrogen (N2) and hydrogen (H2) are the reactants, and ammonia (NH3) is the product.
2. Stoichiometric Coefficients: The coefficients are 1 for N2, 3 for H2, and 2 for NH3. These numbers will be used as exponents in our calculation.
3. Write the Equilibrium Expression: According to the formula for equilibrium constants:
   • K = [Products]^coefficients / [Reactants]^coefficients
   • Therefore, K = [NH3]^2 / ([N2]^1 * [H2]^3)
4. Insert the Concentrations at Equilibrium: Suppose at equilibrium, the concentrations are find to be:
   • [N2] = 0.5 M
   • [H2] = 1.5 M
   • [NH3] = 1.0 M
5. Calculate the Equilibrium Constant:
   • K = (1.0)^2 / (0.5^1 * 1.5^3)
   • K = 1 / (0.5 * 3.375)
   • K = 1 / 1.6875
   • K ≈ 0.593

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