Recording-2025-01-27T04:48:28.898Z

Chemical Reactions and Equilibrium

• Chemical reactions can be reversible, allowing reactants to be converted to products and vice versa.

• At equilibrium, the rates of the forward and reverse reactions are equal, expressed as the equilibrium constant (K).

• The reaction quotient (Q) is used to compare the current state of a reaction to its equilibrium state.

• At a given temperature, a unique equilibrium constant (K) exists for any chemical system.

• If Q does not equal K, the system will shift to restore equilibrium.

Le Chatelier's Principle

• Le Chatelier's Principle states that if a system at equilibrium experiences a change (in concentration, pressure, or temperature), the system will adjust to counteract that change and restore equilibrium.

• It is essential to understand qualitative and quantitative analyses regarding how changes affect equilibrium.

Changes in Concentration

• Increasing Concentration of Reactants:

  • Shifts equilibrium right (toward products) to reduce the concentration of added reactant.

• Decreasing Concentration of Product:

  • Shifts equilibrium right to produce more products until equilibrium is restored.

• Decreasing Concentration of Reactants:

  • Shifts equilibrium left (toward reactants) to increase reactant concentration again.

• Increasing Concentration of Products:

  • Shifts equilibrium left to turn products back into reactants.

Changes in Pressure

• Decreasing Volume (Increasing Pressure):

  • Shift towards the side with fewer moles of gas to reduce pressure.

• Increasing Volume (Decreasing Pressure):

  • Shift towards the side with more moles of gas to increase pressure.

Relationship Between Q, K, and Reaction Rates

• Q vs. K:

  • Changes in concentrations or pressures affect Q, and the system shifts to make Q equal K again.

• Molecular Explanation:

  • More collisions in increased concentrations affect forward and reverse reaction rates.

Temperature Changes

• Effect of Temperature:

  • Unlike concentration or pressure changes, temperature changes impact the value of K.

• Endothermic Reactions (Positive ΔH):

  • Increased temperature behaves like adding a reactant, the system shifts toward products.

• Exothermic Reactions (Negative ΔH):

  • Increased temperature behaves like adding a product, the system shifts toward reactants

Applying Le Chatelier's Principle in Temperature Change

• Example Reaction: N2O4 ⇌ 2NO2

  • If the temperature increases (endothermic), the amount of NO2 will increase as the shifts toward products.

• Quantitative analysis considers how Q changes and equilibrium is reestablished.

Summary

• Le Chatelier's Principle provides a useful framework for anticipating how changes in a chemical system will shift the equilibrium.

• Understanding the underlying reasons related to reaction rates allows for a deeper understanding of chemical equilibria.