7-17. equilibrium

• Explain dynamic equilibrium

  1. ΔG = 0; entropy at max; Gibbs free energy at min
  2. rate of fwd = rate of bkw
  3. closed system
  4. concentration of products and reactants stay constant
• When K < 1, the value of lnK is negative. So −RTlnK is positive. The reaction is non-spontaneous at all temperatures. ΔG becomes more positive as the value of K decreases.
• When K > 1, the value of lnK is positive. So −RTlnK is negative. The reaction is spontaneous at all temperatures. ΔG becomes more negative as the value of K increases.
• Spontaneous reactions:

  1. Gibbs free energy decreases to minimum value at equilibrium
  2. G min = Entropy max (mixtures have higehr entropy than pure substances)
  3. position of equilibrium at products' side
  4. Kc > 1 (due to higher concentration of reactants)

  
• Non-spontaneous reactions:

  1. Gibbs free energy decreases to minimum value at equilibrium
  2. position of equilibrium closer to reactant's side
  3. Kc < 1 (due to higher concentrations of reactants)

  
• When the equilibrium constant K is greater than 1, the ΔG⦵ is negative and the reaction is spontaneous. 
• What is homogenous equilibrium? Equilibrium when both products and reactants are in the same phase
• Which combination of standard change of Gibbs free energy (ΔG⦵) and equilibrium constant (K) is suitable for a reaction that goes to completion?

  Kc >> 1, G = -ve
• Be careful not to confuse the Gibbs free energy change (ΔG) with the standard Gibbs free energy change (ΔG⦵). At equilibrium, the ΔG for a reaction is zero, however, the ΔG⦵ value for a reaction is not necessarily zero unless the equilibrium constant, K, is equal to 1. 
• The equilibrium constant for a particular reaction only depends on the temperature.