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Chemical Equilibrium

Definition of Chemical Equilibrium Reaction

Chemical equilibrium reaction definition suggests the dynamic point between reactant and product for endothermic or exothermic chemical solutions where no further action apart on equilibria at a definite temperatureEquilibrium reaction in solution carried out by changing Gibbs free energy, enthalpy, and entropy of reactant or formation of the product in chemical reactions. Therefore, the equilibrium law suggested the reaction proceeds to some extent than stopping by formation some portion of reactant to the product in the chemical solution. Why does the chemical reaction occur? In a chemical reaction, the reactant or product atoms present in the molecule change their electronic configuration by chemical bonding. But these leading questions for learning chemistry cannot be answered in a simple sentence.

Primarily two factors determine the feasibility of chemical reaction under a given set of conditions. First, the potential energy of the reacting system must be lowered by the reaction. Second, reactants posses potentially to react because they must find a suitable path to react at a participle rate under specific conditions. The first aspect concerns with thermodynamics energy conservation law and discusses under the chemical equilibrium and the second one study under chemical kinetics change of concentration per unit time.

Chemical equilibria or dynamic equilibrium reaction in solution

Formation of Products in Equilibrium Solutions

  1. If hydrogen and iodine vapour kept at a constant temperature in a closed vessel. The reaction proceeds to some extent and then stop, by converting some portion of the hydrogen atom and iodine atom to hydrogen iodide. Because after this dynamic point, the reactant and product attained equilibrium.
  2. If you take some hydrogen iodide in the closed vessel at the same temperature. A faction of hydrogen iodide converted into hydrogen molecule and iodine molecule. Hence the rest of the hydrogen iodide remains unchanged.

But in both the chemistry test, the amount of hydrogen, iodine, and hydrogen iodide remains unchanged. Therefore, the equilibria definition of the chemical reaction maintains the following criteria, approachability from both ends of reactant and product, permanency of the equilibrium, the incompleteness of the reaction, equilibria of the chemical solution.

Equilibrium Solution of Reversible Reaction

When water added to bismuth chloride, a milky solution appears due to the formation of bismuth oxychloride.

BiCl3 + H2O ⇆ BiOCl + 2HCl

But when hydrochloric acid solution added to this milky solution, the milkiness of the solution disappears. This is the example of the dynamic reversible nature of the equilibrium or equilibria.

Heat Change in Equilibrium Chemical Reaction

At the equilibria solution, all reversible chemical reaction, the total specific heat change is zero. But for all irreversible processes or natural chemical reactions, the value of total entropy increases and greater than zero. For example, reduction of stream in presence chemical element iron or diffusion of syrup by water. Therefore, for an irreversible chemical reaction, the total heat change goes to increases. Hence it reached an equilibrium point where the entropy attains maximum value. Because at equilibrium, no further reaction takes place or no further possible entropy change occurs. Hence at equilibrium, ΔStotal = 0.

Exothermic and Endothermic Reactions

All the natural reactions follow a general trend because they take place in a direction that results in an ultimate decrease in the chemical energy of our environment. Thus the exothermic and endothermic reaction differ by definition as

  1. Exothermic chemical reactions are accompanied by the emission of energy.
  2. But endothermic chemical reactions are accompanied by the absorption of energies.

Many exothermic reactions are reversible thus, the reverse process must be endothermic in nature. For example, esterification of acetic acid in an alcohol solution, synthesis of ammonia, and esterification of hydrocarbon amylene (C5H10). If the forward process is an endothermic reversible chemical reaction then the reverse process going through exothermic.

Forward reaction:
2NH3 → N2 + 3H2
(ΔH = +92.22 KJ mol-1)
Backword reaction:
N2 + 3H2 → 2NH3
(ΔH = -92.22 KJ mol-1)

Energy Change in Chemical Reaction

For the spontaneous process, two factors control the ultimate energy change of the reactions, enthalpy change (ΔH), entropy change (ΔS).

But these two changes collectively determined by another fundamental property of the system which known Gibbs free energy (ΔG). Van’t Hoff equation proposed the relation between free energy and the equilibrium constant of a reaction. He used the Gibbs – Helmholtz equation to derive the free energy at the equilibrium.

Problem: Why energy fixed, whether a chemical catalyst used or not?

Solutions: Enthalpy is a state function because ΔH does not change if the initial state and final state are the same. Therefore, according to the Le Chatelier principle, the catalyst cannot change the initial and final state of reactions, hence ΔH remains the same whether a catalyst used or not.

Photochemical Equilibrium Reaction

The chemical equilibrium of the thermal reversible process greatly influences in the forward or backward process by absorption of light or photon energy. Therefore, the absorption electromagnetic spectrum radiation or light by the reactant increases the speed of forwarding reaction but not influence the reverse reaction. Due to increases in products, the rate of the reverse thermal process increases equally. Ultimately balanced the forward or backward reaction to reached equilibrium.

For example, the dimerization of anthracene in the benzene solution carried out photochemical with the spectrum of UV-light. The anthracene in solution irradiated with ultraviolet light and exited by absorbing quantum energy. The exited molecule forms dimer by the collision of the normal molecule. But the exited molecules may also re-emit the absorbed energy through fluorescent and be quenched.

Law of Mass Action and Chemical Equilibrium

Norwegian Physicists, Guldberg, and Waage in 1867 developed the dynamic relationship between the amount of the chemical product or reactant at the equilibrium constant, and this relation is known as mass action law. When temperature kept constant, the rate of a chemical reaction at equilibrium, proportional to the active masses of the reacting system.

For equilibrium systems of chemical reactions of gases or dilute solutions of active mass may be taken as partial pressure and molar concentration solution but for pure crystalline solid active masses taken as unity at equilibria in chemistry. The different physical and chemical definition or measurement uses for determination of the concentration of reactant and product at dynamic equilibria of the exothermic or endothermic reaction such as equilibrium vapour density, refractive index, optical rotation, electrical polarity.