CHEM Equilibrium

• Chemical reactions can be reversible, indicated by a double arrow in the reaction equation
• Reversible reactions have both forward and backward reactions
• At the beginning of the reaction, the forward reaction is fast while the backward reaction is slow
• As the reaction progresses, the rates of the forward and backward reactions equalize, leading to equilibrium
• At equilibrium, the concentrations of reactants and products remain constant
• Concentrations of reactants and products can be different, but as long as the rates of the forward and backward reactions are the same, equilibrium is maintained
• The position of equilibrium can shift depending on conditions:

  • More products indicate equilibrium lies to the right
  • More reactants indicate equilibrium lies to the left
• Equilibrium can only be reached in a closed system where no reactants or products can escape
• Reversible reactions are exothermic in one direction and endothermic in the other
• Example: Thermal decomposition of hydrated copper sulfate to anhydrous copper sulfate and water

  • Forward reaction: Endothermic
  • Backward reaction: Exothermic
• Heating the reaction drives it to the right, evaporating water and forming anhydrous copper sulfate

  • Cooling the reaction drives it to the left, reforming hydrated copper sulfate
• Le Chatelier's Principle is about the position of equilibrium during a reversible reaction and how it's affected by temperature, pressure, and concentration
• The position of equilibrium refers to the ratio of reactant particles to product particles at equilibrium
• If the equilibrium lies to the left, there are more reactants; if it lies to the right, there are more products
• If conditions of a reversible reaction are changed, the position of equilibrium will shift to counteract that change
• Decreasing temperature shifts the equilibrium in the exothermic direction to release heat energy, leading to more products
• Increasing temperature shifts the equilibrium in the endothermic direction to absorb heat energy, leading to more reactants
• Increasing pressure shifts the equilibrium to the side with fewer molecules to reduce pressure
• In the example reaction for ammonia production, increasing pressure shifts the equilibrium to the right (more ammonia)
• Decreasing pressure shifts the equilibrium to the side with more molecules to increase pressure
• In the example reaction for ammonia production, decreasing pressure shifts the equilibrium to the left (more nitrogen and hydrogen)
• Adding more of a reactant increases its concentration, causing the equilibrium to shift to the opposite side to oppose the change
• In the example reaction for ammonia production, adding more nitrogen shifts the equilibrium to the right (more ammonia)