Effect of Pressure Change
In chemical equilibria, pressure changes can profoundly affect gaseous reactions, especially when the number of moles of gaseous reactants differs from that of products. According to Le Chatelier's principle, if an external change is applied to a system at equilibrium, the system will adjust itself to counteract that change and restore a new equilibrium state.
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Pressure and Volume Relationship: When the volume of a gaseous reaction mixture is decreased, the pressure increases, resulting in an equilibrium shift toward the side with fewer gaseous moles. Conversely, increasing the volume lowers the pressure, leading the equilibrium to shift toward the side with more gaseous moles.
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Example Reaction: Considering the reaction:
CO(g) + 3H2(g) ⇌ CH4(g) + H2O(g)
This reaction starts with 4 moles of gaseous reactants (1 CO and 3 H2) and results in 2 moles of gaseous products (1 CH4 and 1 H2O). If the pressure is increased by compressing the volume, the equilibrium will shift to the right (producing more CH4 and H2O).
- Application of the Principle: The principle can also be illustrated using Qc, the reaction quotient. An increase in pressure causes the concentrations of gases to increase, shifting the equilibrium to the side that reduces total moles.
In summary, understanding the influence of pressure on equilibrium is crucial, especially in industrial and laboratory settings, where optimizing conditions can maximize product yield.