Equilibrium

• Many reactions are reversible and exists in a state of equilibrium.
• In a dynamic equilibrium, both the forward and reverse reactions occur at equal rates.
• At equilibrium, there is no change in the concentration of reactants or products.
• A large Kc value ($K_c>1$) implies that products are favored over reactants.
• A small Kc value ($K_c<1$) implies that reactants are favored over products.
• Pure solids and liquids are not included in the Kc calculation. This is because their concentrations barely change throughout the reaction.
• Homogeneous equilibrium


  All reactants and products are present in one phase
• Heterogeneous equilibrium


  Reactants and products are present in more than one phase
• $K_{c \ \text{(reverse)}} =$$\frac{1}{K_{c \ \text{(forward)}}}$
• A catalyst increases both the rate of forward and reverse reaction equally. Hence, there is no effect on the equilibrium position or $K_c$
• Equilibrium constant formula

  $aA+$$bB\rightleftharpoons cC+$$dD$

  $K_c=$$\frac{[C]^c[D]^d}{[A]^a[B]^b}$
• The equilibrium constant is only affected by temperature.
• What affects the equilibrium position?

  • Change in concentration
  • Change in pressure (only if in gaseous state)
  • Change in temperature
• Effect of conditions on equilibrium

  
• Le Chatelier's principle


  If a dynamic equilibrium is disturbed, the equilibrium position shifts to counteract the change and establish a new equilibrium.
• If the concentration of a reactant is increased, the forward reaction will be favored to counteract this. Vice versa.