In the equilibrium 2SO_3 (g) + heat <---> 2SO_2 (g) +O_2 (g)
predict qualitatively the effect of increasing the total pressure and decreasing the temperature. Indicate if the reaction will shift to the right, to the left, or remain unchanged.
When a reaction reaches equilibrium, the forward and reverse reaction takes place at the same rate, and the equilibrium concentration of the reaction mixture does not change as long as we don’t do anything to the system. Le Chatelier’s principle explains what happens if we do anything to disturb the equilibrium. If an external stress is applied to a system in equilibrium, the system reacts in such a way as to partially relieve that stress.
In the equilibrium 2SO_3 (g) + heat <---> 2SO_2 (g) + O_2 (g)
Number of gaseous molecules in the reactant side is lesser. So, on going to the product side pressure increases as more number of gaseous molecules are formed. When the pressure of the system is increased externally, the system reorients itself so that some pressure is reduced. That is done when it reverts back to the reactant side. So, increase of pressure shifts the equilibrium towards left.
The reaction is endothermic. Heat is absorbed as products are formed from reactants and vice versa. When the temperature of the system is decreased by external intervention, the system reorients itself so that some heat is generated. Again, that is achieved when it reverts back to the reactant side. So, decrease in temperature also shifts the equilibrium towards left.
Both the operations are tending to shift the equilibrium to the left. Thus there will be a considerable shift overall.