Chemical energy occurs in such a way that it extract maximum products from the given reactants along with minimizing the energy expenditure. In other words, we can say that a mild temperature and pressure, can yield a maximum number of products. For example, if we take Haber’s process in which ammonia is synthesized from N2 and H2 the economic conditions is kept in mind. Because about hundred million tones of ammonia are produced every year for fertilizers and hence, efficiency plays a major role here.
The equilibrium constant Kc does not depend upon the initial condition. But if the concentration of one or more substance is changed then the overall system is no more at equilibrium and the net reaction proceeds in a certain direction. To know about the overall change in the reaction we use Le Chatelier’s principle.
According to Le-Chatelier’s principle, if there is any change in the factors that affect the equilibrium conditions of the system, the system will counteract or reduce the effect of the overall change. This principle is applicable for both physical as well as chemical equilibrium. In this state, the rate of the forward reaction is equal to the rate of backward reaction. There are several factors like temperature, pressure, and concentration of the system which affect equilibrium.
The Factors Affecting Equilibrium are discussed below.
Change in concentration:
According to Le-Chatelier’s principle, we can predict that there is a shift in equilibrium when it’s is disturbed by addition or removal of reactants or products.
- The concentration of the reactants or products added is relieved by the reaction which consumes the substance which is added.
- The concentration of reactants or products removed is relieved by the reaction which is in the direction that replenishes the substance which is removed.
- When the concentration of the reactant or product is changed, there is a change in the composition of the equilibrium mixture.
Change in pressure:
Change in pressure happens due to the change in the volume. If there is a change in pressure it can affect the gaseous reaction as the total number of gaseous reactants and products are now different. According to Le Chatelier’s principle, in heterogeneous equilibrium, the change of pressure in both liquids and solids can be ignored because the volume is independent of pressure.
Change in Temperature:
The effect of temperature on equilibrium depends upon the sign of ΔH of the reaction and follows Le-Chatelier’s Principle.
- As temperature increases the equilibrium constant of an exothermic reaction decreases.
- In an endothermic reaction the equilibrium constant increases with increase in temperature.
Along with equilibrium constant, the rate of reaction is also affected by the change in temperature. As per Le Chatelier’s principle, the equilibrium shifts towards the reactant side when the temperature increases in case of exothermic reactions, for endothermic reactions the equilibrium shifts towards the product side with an increase in temperature.
Effect of a Catalyst:
A catalyst does not affect the equilibrium of a system. It only speeds up a reaction. In fact, it equally speeds up the forward as well as the reverse reaction. This results in the reaction reaching its equilibrium faster. Same amount of reactants and products will be present at equilibrium in a catalyzed or a non-catalysed reaction. The presence of a catalyst only facilitates the reaction to proceed through a lower-energy transition state of reactants to products.
Effect of addition of an Inert Gas
When an inert gas like argon is added to a constant volume it does not take part in the reaction so the equilibrium remains undisturbed. Because in a reaction when we add inert gas at constant volume, it does not change the partial pressures or molar concentrations of the substances. If the gas added is a reactant or product involved in the reaction then the reaction quotient will change.
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