Chemical Equilibrium - SS2 Chemistry Past Questions and Answers - page 2

Le Chatelier's Principle states that when a system in equilibrium is subjected to a change in conditions, the system will adjust to counteract the change and establish a new equilibrium. It helps predict the direction in which an equilibrium system will shift when changes are imposed on it.

Le Chatelier's Principle can be applied to changes in temperature, pressure, and concentration to understand the effect on equilibrium systems. Here are a few examples:

a.    Temperature Change: When the temperature of an equilibrium system is increased, the system will shift in the direction that absorbs heat (endothermic reaction). Conversely, if the temperature is decreased, the system will shift in the direction that releases heat (exothermic reaction). For example, in the Haber-Bosch process for ammonia synthesis, increasing the temperature decreases the yield of ammonia (NH3) because the reaction is exothermic.

b.    Pressure Change: Changes in pressure affect equilibrium systems involving gases. An increase in pressure will cause the system to shift in the direction that reduces the number of moles of gas, while a decrease in pressure will cause the system to shift in the direction that increases the number of moles of gas. For instance, in the reaction between nitrogen dioxide (NO2) and dinitrogen tetroxide (N2O4), increasing the pressure favours the formation of N2O4 since it has fewer gas molecules.

2NO2(g) ⇌ N2O4(g)

c.     Concentration Change: Altering the concentration of reactants or products can influence equilibrium. If more reactants are added, the system will shift in the direction that consumes the added reactants. Conversely, if more products are added, the system will shift in the direction that consumes the added products. For example, in the equilibrium between carbon monoxide (CO) and hydrogen gas (H2) in the synthesis of methanol, adding more CO will cause the system to shift towards the production of methanol.

CO(g) + 2H2(g) ⇌ CH3OH(g)

Le Chatelier's Principle provides a useful framework for predicting and understanding the response of equilibrium systems to changes in temperature, pressure, and concentration. It helps in optimising reaction conditions to maximise desired products or yield. By applying Le Chatelier's Principle, scientists and engineers can manipulate equilibrium systems to enhance efficiency and desired outcomes in various chemical processes.