Chapter 11 - Further Equilibrium

• A homogenous reaction is a reaction where all reactants and products are in the same phase.
• A heterogenous reaction is a reaction in which at least one of the reactants and/or products is in a different phase to the others.
• The ‘c’ in Kc means that the value is calculated using the concentrations of the reactants and products.
• Kc is a constant at equilibrium at a given temperature.
• Solid reagents/products are not included in the Kc expression because the concentration of a solid at a given temperature is determined by its density, which is a constant.
• Partial pressure is the pressure that an individual gas (within a mixture of gases) would exert if it alone occupied the volume of the mixture.
• The total pressure of a mixture equals the sum of the partial pressures of all the gases present in the mixture.
• The ‘p’ in Kp means that the value of the constant is calculated using the partial pressures of the gaseous reagents/products.
• The partial pressure of an individual gas in a mixture of gases is calculated by multiplying its mole fraction by the total pressure.
• The mole fraction of a gas ‘A’ can be calculated by number of moles of A/total number of moles of gas.
• For solids that are in equilibrium with gases, the partial pressures of the solids are not included in the Kp expression.
• Although Kc remains constant at equilibrium (unless the temperature changes), the reaction quotient (Qc) will respond to changes in concentration.
• When Qc and Kc are no longer equal, the equilibrium composition will change to make them equal again.
• Changes in pressure have no effect on Kp or Kc. However, if the total pressure of a system changes, then the partial pressures of the individual gases will change.
• A catalyst doesn’t appear in the overall equation for a reaction, therefore it has no influence on Kc or the position of equilibrium. Instead, catalysts increase the rate at which equilibrium is achieved.