Is Chemical Equilibrium A System: 7 Facts You Should Know


In this article, we should learn about the chemical equilibrium of any reaction and Le Chatelier’s principle is chemical equilibrium a system.

Sometimes all the reactions did not go completed if the suitable conditions are applied to them. After some time the reaction will be stopped by leaving some amount of reactant. Actually, they go to some extent and then stopped, because at that stage they stopped they have attained already a state of equilibrium. So, on applying conditions does not change the reaction and they do not go forward or backward direction, then we have to apply the different experimental conditions.

The rate of reaction for both forward and backward are equal at the equilibrium state The nature of the equilibrium is dynamic for a chemical equilibrium following points are to be noted is chemical equilibrium a system.

  1. the equilibrium is dynamic
  2. equilibrium can be reached from both directions.

1.    What is chemical equilibrium?

Let us consider a reversible reaction that occurs in a closed vessel at a constant temperature condition;

is chemical equilibrium a system
A Equilibrium Reaction

The rate of this chemical reaction at a constant temperature depends on the relative amount or concentration of the reactants only. An increase in concentration increases the reaction rate while a decrease in concentration decreases the rate of the reaction.

In the beginning, the reaction system neither contains C nor D but contains A and B. So, the reaction proceeds only in the forward direction. In this situation, the concentration of reactants is high, so, the rate of the reaction becomes maximum is chemical equilibrium a system.

As soon as C and D start forming in the forward reaction, they interact with each other to produce A and B again. At the beginning of the reaction, the concentration of C and D is very very low, so the rate of the backward reaction is also negligible at that moment is chemical equilibrium a system.

But as the concentration of C and D goes on increasing with time, the rate of the backward reaction also increases. On the other hand, with the rise in the concentration of C and D, the concentration of A and B gradually decrease. As a result, the forward reaction rate decreases progressively. After going through this process when a moment comes when the rate of the forward reaction and backward reaction becomes equal at the equilibrium state is chemical equilibrium a system.

Graph of Concentration vs. Time in a Reversible Reaction

The equilibrium state only exists in any reaction when the rate of forward reaction and the rate of backward reaction becomes equal. In this condition, the reaction does not reach a state of total stagnation. Both the forward and backward reactions proceed simultaneously at the same rate of reaction for a particular reaction.

At equilibrium, the concentration of the different constituents present in the reaction system is called equilibrium concentration and the whole mixture is known as the equilibrium mixture. If the conditions (i.e. temperature, pressure, etc.) of the reaction are kept constant, the relative amounts of the various constituents present in the reaction system do not change with time is chemical equilibrium a system.

Definition of chemical equilibrium

At a given temperature and pressure, when in any reversible chemical reaction, the speed of the forward reaction and speed of the backward reaction becomes equal to the reverse reaction and the relative amount of the various constituents present in the reaction system does not change with time, then that particular state is called the state of the chemical equilibrium of that particular reaction is chemical equilibrium a system.

After the establishment of equilibrium of any reversible chemical reaction, if the reaction system is left to stand for an indefinite period at constant temperature and pressure, then the relative amount of the reactants and the products will remain unaltered is chemical equilibrium a system.

This observation leads to the impression that the reaction stops completely at equilibrium is chemical equilibrium a system.

But it has been proved experimentally that the reaction has not ceased, rather both the forward and the backward reactions proceed simultaneously at the same rate.  

That is why chemical equilibrium is designated as dynamic equilibrium.

2.    Why is chemical equilibrium a system?

Before starting why is chemical equilibrium a system exists we should discuss the factor affecting chemical equilibrium.

Permanency of chemical equilibrium

There is no change in its equilibrium if the physical and chemical condition of that reaction remains unchanged i.e., equilibrium is characterized by constancy in the concentration of the reactants and the products also. But the change in the condition of the reaction can change the state of equilibrium is chemical equilibrium a system.

Dynamic nature of equilibrium

Even after the attainment of equilibrium, the chemical reactions do not cease. At equal or the same speed the forward and the reverse reactions proceed simultaneously.

When the rate of the forward reaction and the rate of the backward reaction in any reversible chemical reaction becomes equal, only then the reaction attains equilibrium or at that moment we can say that the reaction exists in its equilibrium state So, at equilibrium, if any one of the forward and reverse reactions becomes 100% complete, the equilibrium itself loses its existence. Hence for the equilibrium to exist, the reactions of both directions will have to be incomplete is chemical equilibrium a system.

Approachability of equilibrium from either direction

When a reversible chemical reaction is started under a certain set of conditions, either with the reactants or products of that reaction, the same equilibrium will be attained, i.e., it does not matter whether the starting materials are the reactants or the products, provided the experimental conditions are identical in both the cases is chemical equilibrium a system.

A catalyst cannot alter the state of equilibrium

The equilibrium state attained in the case of any reversible chemical reaction in the presence or absence of a catalyst is always found to be the same, provided the conditions during the reactions are identical. In other words, the relative amount of the reactant and the product remain the same whether a catalyst is used or not is chemical equilibrium a system.

Catalysts can speed up the reaction rate only but maintain the equilibrium.

3.    When a system is in chemical equilibrium?

When in any reaction the concentration of reactants and concentration of products are equal by application of temperature or pressure or even concentration then the system is in equilibrium.

Two systems exist where is a chemical equilibrium a system occurs

Homogeneous equilibrium

The equilibrium of any chemical reaction in which all the substances, reactants as well as products, are in the same phase or same physical state is known as homogeneous equilibrium.

N2(g) + 3H2(g) = 2NH3(g)

Heterogenous equilibrium

The equilibrium of any chemical reaction in which the reactants and products are in different phases or different physical state is known as heterogeneous equilibrium.

CaCO3(s) = CaO(s) + CO2(g)

4.    Is chemical equilibrium a closed system?

In a closed system, any reversible reaction will reach a state of equilibrium. Actually,  in a closed vessel it is chemical equilibrium a system occurs.

A reversible reaction is known as where the products are obtained by the interaction between the reactants, react with each other to form the reactants, and an equilibrium is set up between the reactants and the products under the conditions of the reaction.

In a closed vessel thermal decomposition of NH4Cl is a reversible reaction is chemical equilibrium a system.

When NH4Cl is heated in a closed vessel at 3500C, it undergoes thermal decomposition to produce NH3 and HCl gases. But, even after a prolonged period, it is observed that besides NH3 and HCl gases undecomposed NH4Cl vapor remains in the container. This proves that the decomposition of NH4Cl vapor by the application of heat never gets completed is chemical equilibrium a system.

In another closed vessel, an equimolar mixture of NH3 and HCl gases is heated at 3500C for a prolonged period, and the vessel is found to contain NH4Cl vapor along with NH3 and HCl gases. That is the reaction between NH3 and HCl gases in a closed vessel never gets completed is chemical equilibrium a system.

Thus, it can be concluded that NH4Cl vapor decomposes on heating to produce gaseous NH3 and HCl which again react partially with each other to reform NH4Cl gas under the given conditions of the reaction. In other words, the thermal decomposition of NH4Cl vapor is a reversible reaction.

Characteristics of a reversible reaction

The main and only characteristic of a reversible reaction is the forward and backward reactions occur simultaneously. In the forward reaction, reactants react with each other to yield the products, while the products interact with each other to produce the reactants in the backward reaction is chemical equilibrium a system.

Due to the incompleteness of a reversible reaction, the reactants never get exhausted in such reactions.

In such reactions, an equilibrium state only exists when the rate of the forward reaction and the rate of the backward reaction becomes equal in that particular reaction and no alter occurs.

For the reversible reaction, at the equilibrium state, the change in Gibbs’s free energy is zero.

5.    Can chemical equilibrium occur in an open system?

To show whether a reaction stays in chemical equilibrium in the open system we consider reaction. Most of the reactions are found to be irreversible when conducted in open containers but if the same reactions are performed in closed containers, seem to be reversible reactions.

When solid CaCO3 is heated in an open container

If the heating is done in an exposed condition, CO2 gas escapes from the container into the air and only solid CaO remains as a residue. In this case, the reactant is completely exhausted. So, the reaction is considered an irreversible reaction, and no chemical equilibrium is observed is chemical equilibrium a system.

So, there is no equilibrium existing in the concentration of products, so in an open system, chemical equilibrium does not exist. Actually, mass and heat both are escapes here.

6.    How to find the chemical equilibrium of a system

On the basis of the law of mass action, we can predict the equilibrium of a chemical reaction that follows stoichiometric calculation. In detail, we can calculate the equilibrium constant instead of the chemical equilibrium of reactions. Laws of mass action can be defined depending on the reaction rate on the concentration of the reactant of a stoichiometric reaction.

let us consider the following chemical reaction one gram-mole of A reacts with one gram-mole of b to produce one gram-mole of C: A+B = C

So, according to the law of mass action, at a definite temperature at a particular moment, the rate of reaction, is chemical equilibrium a system.

  r α [A][B], or r =k[A][B]

where k is proportionality constant, known as rate constant. [A] and [B] are the active masses or molar concentrations of A and B respectively at that moment.

Now comes in different rate equilibrium constant depends on concentration, pressure, and molar concentration.

Kc – if the active masses of the components participating in any reversible chemical reaction at equilibrium are expressed in terms of the molar concentration, then the equilibrium constant obtained is called kc.

aA+bB = dD+eE

kc = [D]d*[E]e/[A]a*[B]b where [A], [B], [D], [E] are the molar concentration of different constituents at equilibrium.

Kp – If the active masses of the components participating in any reversible gaseous reaction at equilibrium are expressed in terms of partial pressure, then the equilibrium constant so obtained is known as kp.

aA(g)+bB(g) = dD(g)+eE(g)

Kp = pdD*peE/paA*pbB where pA, pB, pD, pE  are the partial pressures of the different constituent gases at equilibrium respectively.

Kx – the equilibrium constant of any reversible chemical reaction, obtained by expressing the molar concentration of the reactants and the products in terms of their mole fraction, is designated as kx.

aA+bB = dD+eE

kx= xdD*xeE/xaA*xbB where xA, xB,xd,xE are the mole fractions of A,B,D and E respectively at equilibrium.

7.    Le Chatelier’s principle

If a system under equilibrium is subject to a change in pressure, temperature or concentration, or other physical parameters then the equilibrium will shift itself in such a way as neutralizes the effect of that change.

Factors affecting Le Chatelier’s principle,

  • Effect of increasing and decreasing pressure
  • Effect of increase and decrease temperature
  • Effect of catalyst on equilibrium
  • Effect of addition of inert gas on equilibrium

Conclusion

Every reversible reaction tries to attain an equilibrium state. This equilibrium state occurs due to the presence of temperature, pressure, the concentration of reactants, and even catalysts also.

Biswarup Chandra Dey

Chemistry is not all about reading line by line and memorize, it is a concept to understand in easy way and here I am share with you the concept about chemistry which I learn because knowledge is worth to share it.

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