Question

State Le-Chatelier's principle.

Answer 1

Le Chatelier’s principle governs the possibility of the changes and also the effects of the changes that can take place when any of the components of the reaction such as the concentration of the reactants and products, the temperature, pressure etc., have been changed when the reaction has already achieved equilibrium.

Complete step by step solution:
Le Chatelier's principle applies to the chemical or physical systems in equilibrium. It states that a change in any of the factors that determine the equilibrium condition of a substance system will cause the system to change in such a manner to reduce or to counteract the effect of a change.
In simple words, after a reaction has achieved equilibrium, if we change any of the physical or chemical components of the reaction, the equilibrium will shift in such a way that it counteracts or reduces the effect of the change that we have made on the system.
Let us look into some of the physical and chemical components which we can change that in the equilibrium state of a reaction and let us also check how it counteracts the change to minimize the effect of the change:
-Effect of concentration change: The concentration change can take place by two means, one is by removal of the reactants or products another is by addition of reactants or products. When any of the reactants are removed, according to Le Chatelier's principle, the equilibrium will shift towards the left-hand side (backwards) i.e. it will create more reactants to minimize the change.
This is also true for the addition of reactants as well as the addition or removal of products.
-Effect of pressure and volume changes: It is a change which is obtained by changing the volume that can affect the yield of the product in case of a gaseous reaction when the total number of moles of gaseous reactants and the total number of moles of gaseous products are different.
Le Chatelier's principle does not account for a heterogeneous equilibrium in case of pressure or volume changes because the effect of pressure changes on solid and liquid is negligible as the volume of a solution or liquid is nearly independent of pressure.
-Effect of inert gas addition: When an inert gas is added to an equilibrium system keeping the volume constant, the total pressure will increase. But this will not affect the equilibrium because the number of moles of the reactants and products i.e. the concentration of the reactants and products will remain the same. Thus no change will occur.
But if we add inert gas at constant pressure, the total volume will increase. This will result in a decrease in the number of moles per unit volume or concentration. Then the system will react in such a way to move the equilibrium in the direction where the number of moles is more.
-Effect of change in temperature: If we increase the temperature of the reaction the system will react in such a way that helps in decreasing the temperature. If the reaction is an exothermic reaction i.e. it produces heat energy, increasing the temperature will shift the reaction towards the reactant’s side and the reverse is true in the case of endothermic reactions.

Let's take the example of Haber’s process:

\overset{Fe}{\rightleftharpoons}\underset{Ammonia}{\mathop{2N{{H}_{3}}}}\,\text{ }+\text{ Heat}$$ -Increase in reactant concentration: The increase in the concentration of the reactants will lead to the formation of more products as the increase in the concentration of the reactants will be compensated by the increase in the concentration of the products. -Pressure Increase: Here we can see that there are a total 4 (3 + 1) moles on the reactants side and 2 moles on the products side. Now, if we increase the pressure, the system will react in such a way that it will favour the reaction which produces less number of moles. This indicates that the equilibrium will shift towards the right-hand side i.e. the product side. -Addition of inert gas: Adding inter gas at constant pressure in the case of Haber’s process will favour the backward reaction i.e. the ammonia will break into nitrogen and hydrogen since the number of moles is greater in the reactant’s side compared to the product side. -Decrease in temperature: As we can see that this process produces heat. Thus decrease in temperature will favour the forward reaction where more heat is produced and thus more ammonia will be produced. **Note:** This principle not only helps us in understanding the effects of change in the equilibrium state of a reaction but also helps us to calculate what components of the reaction in any manufacturing process can be changed to get a good amount of yield of products. Just like we saw in Haber’s process that increasing pressure and decreasing temperature can yield more ammonia, we can use this principle for other industrial manufacturing processes as well.