Effect of Change in Temperature on Equilibrium
According to Le Chatelier’s Principle, the position of equilibrium moves in such a way as to tend to undo the change that we have made. If we increase the temperature, the position of equilibrium will move in such a way as to reduce the temperature again and it will be done by favoring the reaction which absorbs heat. A rise in temperature favors the endothermic reaction as the heat speeds up the rate of reaction by providing sufficient energy to reactant molecules to complete reaction faster.
Le Chatelier’s Principle for temperature change is governed by the following equation:
log[k1/k2] = -â–³H/R[{1/T2}-{1/T1}]
where,
- k is equilibrium Constant
- â–³H is change in enthalpy
- T is Temperature
- R is gas constant
According to this relation, increase in temperature will decrease k2 and vice versa.
As per Le Chatelier’s Principle, increase in temperature shifts the equilibrium in the direction of endothermic reaction and decrease in temperature shifts the equilibrium in the direction of exothermic reaction.
- â–³H > 0 (Heat is absorbed): Endothermic reaction in which increase in temperature will shift the reaction towards right.
- â–³H < 0 (Heat is evolved): Exothermic reaction in which increase in temperature will shift the reaction towards left.
Let’s see some examples of this
High temperature favors forward reaction owing to its endothermic nature. In this case, the equilibrium will shift in backward direction and there will be decrease in product
N2(g) + O2(g) ⇄ 2NO (g); △H = +180 KJ (Heat is absorbed)
PCl5(g) ⇄ PCl3(g) + Cl2(g); △H = +63 KJ (Heat is absorbed)
Low temperature favors forward reaction owing to its exothermic nature. In this case, the equilibrium will shift in forward direction and there will be increase in product formation.
H2(g) + I2(g) ⇄ 2HI(g) ; △H = -10.4 KJ (Heat is evolved)
N2(g) + 3H2(g) ⇄ 2NH3(g) ; △H = -93.6 KJ (Heat is evolved)
2SO2(g) + O2(g) ⇄ 2SO3(g) ; △H = -189 KJ (Heat is evolved)
Le Chateliers Principle
Le Chatelier’s Principle is a fundamental concept in chemistry that describes how a chemical system at equilibrium responds to changes in temperature, pressure, or concentration of reactants or products. This principle is named after the French chemist Henry Louis Le Chatelier, who formulated it in the late 19th century. Equilibrium refers to the state of balance which tells that there is equal weight on both sides of the scale. Chemical equilibrium is attained when the rate of forward reaction is equal to the rate of backward reaction.
In this article, we will have a thorough knowledge of equilibrium, Le Chatelier’s principle, and the effect of various factors on chemical equilibrium.
Table of Content
- What is Le Chatelier’s Principle of Equilibrium?
- Effect of Concentration Change on Equilibrium
- Effect of Change in Pressure on Equilibrium
- Effect of Volume Change on Product Formation
- Effect of Change in Temperature on Equilibrium
- Effect of Catalyst on Equilibrium
- Effect of Addition of an Inert gas on Equilibrium
- Application of Le Chatelier’s Principle