Chemical Equilibrium: Principles and Applications
Classified in Chemistry
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Reversible Reactions
In general, all chemical reactions are reversible. External conditions determine the activation energy for each direction; when the activation energy for one direction is significantly lower than the other, that specific reaction pathway is favored.
Chemical Equilibrium States
Chemical equilibrium occurs when the rate of formation of products equals the rate of formation of reactants. The specific conditions required to reach equilibrium depend on the individual reaction.
Law of Mass Action
The speed of a reaction is proportional to the product of the active masses of the reactants.
The Equilibrium Constant
The equilibrium constant (Ke) is defined as the product of the concentrations of the products divided by the product of the concentrations of the reactants, each raised to the power of their respective stoichiometric coefficients.
- If Ke < 1, the formation of reactants is favored.
- If Ke > 1, the formation of products is favored.
Types of Chemical Equilibrium
- Homogeneous Equilibrium: Occurs when all compounds are present in a single phase.
- Heterogeneous Equilibrium: Occurs when the equilibrium involves more than one phase, such as a solid immersed in a liquid.
Le Chatelier's Principle
In the late nineteenth century, the French chemist Henry Le Chatelier postulated that if a system at equilibrium is subjected to a change, the system will adjust to counteract that change.
Effect of Temperature
The equilibrium constant is specific to a given temperature. Therefore, a change in temperature directly affects the value of Ke for the reaction.
Effect of Pressure
Pressure variations in a system at equilibrium significantly affect gaseous substances. Changing the pressure alters the volume, which changes the concentration (or partial pressure) of the species present.
Applications of Le Chatelier's Principle
Industrially, this principle is used to optimize reaction conditions to maximize product yield by carefully controlling pressure, temperature, and the concentration of the involved reactants.