Chapter 17 Chemical equilibrium：17章化学平衡.ppt

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Heterogeneous Equlibria What are the forms of Kc and Kp? SO2(g) + H2O(l) ? H2SO3(aq) at 25oC Kc= [SO2] [H2SO3] Kp= PSO2 1 H2O(l) is the solvent 水溶液不因壓力改變而有所變化 * Heterogeneous Equlibria What are Kc and Kp for this reaction? CaF2(s) ? Ca2+(aq) + 2F1-(aq) at 25oC Kc = [Ca2+][F-]2 Kp is not defined; no gas involved 3Fe(s) + 4H2O(g) ? Fe3O4 (s) + 4H2(g) at 500oC Kc= [H2O]4 [H2]4 Kp= (PH2O)4 (PH2 )4 Heterogeneous Equlibria * Example 17-15: Kc and Kp for Heterogeneous Equlibria Write both Kc and Kp for the following reversible reactions. 2ZnS(s) + 3O2(g) ? 2ZnO(s) + 2SO2(g) 2NH3(g) + H2SO4(l) ? (NH4)SO4(s) S(s) + H2SO3(aq) ? H2S2O3(aq) a. Kc= [O2]3 [SO2]2 Kp= (PO2)3 (PSO2 )2 b. Kc= [NH3]2 1 Kp= (PNH3)2 1 c. Kc= [H2SO3] [H2S2O3] Kp: undefined, no gases involved * Spontaneity of Physical and Chemical Changes (Ch15, p575) Spontaneous changes happen without any continuing outside influences. 自發性的改變指不受任何外力影響下所進行的 A spontaneous change has a natural direction. For example the rusting of iron occurs spontaneously. (例如鐵生琇) Have you ever seen rust turn into iron metal without man made interference? The melting of ice at room temperature occurs spontaneously. (又如冰在室溫中溶化) Will water spontaneously freeze at room temperature? * The Two Aspects of Spontaneity 自發性反應的兩個概念 An exothermic reaction does not ensure spontaneity.(放熱反應並不能確保為自發性反應) For example, the freezing of water is exothermic but spontaneous only below 0oC. An increase in disorder of the system also does not insure spontaneity.(增加系統的亂度亦不能確保為自發性反應) It is a proper combination of exothermicity and disorder that determines spontaneity.(需放熱及亂度的適當組合才能決定反應是否為自發性反應) * Entropy熵, S Entropy is a measure of the disorder or randomness of a system.熵用以測定一個系統的亂度 As with ?H, entropies have been measured and tabulated in Appendix K as So298.熵可被測量如附表K When: ?S 0 disorder incre