A shift refers to a change or adjustment in the position or state of an equilibrium system in response to a change in one of the conditions affecting the system. This concept is central to understanding Le Châtelier's Principle, which describes how a system at equilibrium will respond to external disturbances.
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A shift in an equilibrium system occurs when a change in a condition, such as concentration, temperature, or pressure, is applied to the system.
The shift in the equilibrium position is a response by the system to counteract the change and re-establish a new equilibrium state.
The direction of the shift is determined by Le Châtelier's Principle, which states that the system will shift to oppose the change and minimize the disturbance.
The magnitude of the shift depends on the strength of the change in the condition and the equilibrium constant of the reaction.
Shifts in equilibrium can affect the concentrations of reactants and products, as well as the overall yield of the reaction.
Review Questions
Explain how a shift in equilibrium occurs in response to a change in concentration of a reactant or product.
According to Le Châtelier's Principle, if the concentration of a reactant or product in an equilibrium system is changed, the system will shift to counteract the change and re-establish equilibrium. For example, if the concentration of a reactant is increased, the system will shift to the right, producing more products to decrease the reactant concentration and re-establish the equilibrium. Conversely, if the concentration of a product is increased, the system will shift to the left, consuming more products and producing more reactants to offset the change.
Describe how a shift in equilibrium occurs in response to a change in temperature, and explain the relationship between the direction of the shift and the enthalpy of the reaction.
According to Le Châtelier's Principle, if the temperature of an equilibrium system is increased, the system will shift to counteract the change and re-establish equilibrium. If the reaction is exothermic (releases heat), the system will shift to the left to consume the excess heat and lower the temperature. If the reaction is endothermic (absorbs heat), the system will shift to the right to produce more heat and raise the temperature. The direction of the shift is determined by the enthalpy of the reaction, with the system shifting to favor the direction that minimizes the temperature change.
Analyze how a shift in equilibrium occurs in response to a change in pressure, and explain the relationship between the direction of the shift and the number of moles of gas in the reaction.
According to Le Châtelier's Principle, if the pressure of an equilibrium system is increased, the system will shift to counteract the change and re-establish equilibrium. The direction of the shift will depend on the number of moles of gas in the balanced chemical equation. If the reaction has a greater number of moles of gas on the product side, the system will shift to the reactant side to decrease the number of moles of gas and lower the pressure. Conversely, if the reaction has a greater number of moles of gas on the reactant side, the system will shift to the product side to increase the number of moles of gas and raise the pressure. The system will always shift in the direction that minimizes the change in pressure.
A state of balance where the forward and reverse reactions in a system occur at the same rate, resulting in no net change in the concentrations of reactants and products.
A principle that states that when a system at equilibrium is subjected to a change in one of the factors (concentration, temperature, or pressure) affecting the equilibrium, the system will shift to counteract the change and establish a new equilibrium.
Disturbance: Any change in the conditions (concentration, temperature, or pressure) of an equilibrium system that causes the system to shift in order to reestablish equilibrium.