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Study chemical equilibrium and reaction in chemistry

Why do chemical reactions occur? This leading question in study chemistry can not be answered in a simple sentence Details study reveal that the two primary factor responsible for the feasibility of a chemical reaction.
  1. The potential energy of the reacting system must be lowered by the reaction.
  2. Reactants posses potentially to react, they must find a suitable path to react at a participle rate under specific conditions.
The fast concern with the thermodynamics and study it under chemical equilibrium and the second one constitute the study of chemical kinetics.

Energies of a chemical reaction

All the natural process follow a general trend that they take place in a direction which results in an ultimate decrease in the energy of the universe.
  • The release of energy in a chemical reaction is readily demonstrated by the exothermic reaction.
  • Endothermic reactions are accompanied by the absorption of heat.
Many exothermic reactions are reversible and the reverse process must be endothermic in nature. The synthesis of ammonia is an endothermic reversible reaction.
  • Forward reaction: N₂ + 3H₂ → 2NH₃ ΔH = -92.22 kJ mol⁻¹.
  • Backword reaction: 2NH₃ → N₂ + 3H₂ ΔH = +92.22 kJ mol⁻¹.
Evaluation of heat can not be considered the necessary driving property of a chemical reaction. To study the spontaneous process of a chemical reaction two factors control the ultimate energy change of the chemical process.
  1. Enthalpy change (ΔH).
  2. Entropy change (ΔS).
These two changes collectively determined by another fundamental property of the system known Gibbs free energy (ΔG).

Van't Hoff proposed the equilibrium point of a chemical reaction is constant at a given temperature. The quantitative relation between equilibrium and Gibbs free energy by using the Gibbs - Helmholtz equation.

The equilibrium point of a chemical reaction

A chemical reaction can not be completed if the favorable external condition not maintained. The reaction proceeds to some extent and they stop by converting some portion of reactant to product.

If hydrogen and iodine vapor kept at a constant temperature in a closed vessel, only a portion of hydrogen and iodine converted into hydrogen iodide and then the reaction is stopped.

H₂ + I₂ ⇆ 2HI

If at the same temperature some hydrogen iodide is taken in the closed vessel, a faction of hydrogen iodide converted into hydrogen and iodine and rest of hydrogen iodide remain unchanged.

The amount of hydrogen, iodine, and hydrogen iodide remail unchanged in both the experiment.
When a chemical reaction reached such a stage that no further action is apert is called the equilibrium point of the chemical reaction.

The equilibrium point of the chemical reaction maintains the following criteria
  1. Approachability from both ends.
  2. Permanency of the equilibrium point.
  3. The incompleteness of the reaction.
  4. Dynamic nature of the equilibrium point.

Hydrolysis of bismuth chloride

Water is added to the bismuth chloride solution, the milky-like solution appears due to the formation of bismuth oxychloride.

BiCl₃ + H₂O ⇆ BiOCl + 2HCl

If hydrochloric acid solution added the milkiness disappears showing the reversible reaction occurs.
This shows the reversible nature of this chemical reaction.

Justify or criticize the following: the heat of reaction is the same whether a catalyst used or not.


H is a state function hence ΔH (heat of a reaction) does not change if the initial state and final state of a process are the same.

A catalyst cannot change the initial and final state of a chemical reaction, hence ΔH remains the same whether a catalyst is used or not. Therefore the statement is correct.

Law of mass action from the equilibrium point

Norwegian Physicists, Guldberg and Waage in 1867 developed the quantitative relation between the amount of the reactant and product at equilibrium point is known as mass action law.

At constant temperature, the rate of a chemical reaction is proportional to the active masses of the reacting system.
  1. Molar concentration (moles/lit) when the solution is dilute.
  2. Partial pressure in the atmosphere unit for the gaseous system.
  3. For pure solid and pure liquid, active mass is assumed to be unity.
Chemical Equilibrium Questions and Answers
Chemical equilibrium
More details study of Law of mass action online

Study chemical equilibrium reaction in chemistry online for school and college courses, energies, equilibrium point, and the law of mass action

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