14 Chemical Equilibrium - Science：14化学平衡的科学.ppt

16 Chemical Equilibrium A System Chemical Equilibrium – a dynamic process Some Typical Equilibria The reaction quotients Expressions for reaction quotients More expressions for reaction quotients Equilibrium constant - mass action law Evaluating K Evaluate quantities Evaluate quantities Entropy Entropy calculation Josiah W. Gibbs Gibbs free energy, G or ?G Energy and equilibrium constant K More expressions for equilibrium constant An Example Analysis of Example Calculate Kc Evaluate KcCompare with slide 41 Application of Kc Trial and error or Newtons method Apply math skill Successive approximation Equilibria involving solvents Equilibria involving solvents - application Equilibrium Calculations – a summary Kp and Kc; Kp = Kc (R T) {c+d-(a+b)} Kp more appropriate for Kc and Kp conversion Le Chatelier’s Principle Le Chatelier’s Principle – cont. Henri Louis Le Chatelier Effect of a catalyst Equilibria - Summary Equilibrium review -1 Equilibrium review – 2 Compare with slide 23 Equilibrium review - 3 Equilibrium review - 3 Several methods have been introduced in evaluating x Simple methodApproximationTrial and error (Newtons method)Recognize math relationship (taking square root on both sides)Successive approximation The equilibrium constants depends on the units used for quantities. In general, the equilibrium constant is represented by K When concentrations are used, Kc is the notation;when partial pressures are used, Kp is used Since PV = n R T, P = (n/V) R T = [ ] R T [ ] = (n / V) is the concentration For the reaction a A + b B ? c C + d D PCc PDd [C]c [D] d (R T)c + d Kp = ———— = ———————— = Kc (R T){c+d-(a+b)} PAa PBb [A]a [B] b (R T)a + b See page 635 H2O (l) = H2O (g) Kp = vapor pressure of water H2O (s) = H2O (g) Kp = vapor pressure of ice At the triple point, it’s obvious that vapor pressure of ice = vapor pressure of waterif these are equal, the three phases are present. CaCO3 (s) = CaO + CO2 Kp = partial v