tailieunhanh - Ebook Instant notes - Inorganic chemistry (2nd edition): Part 2

(BQ) Part 2 book "Instant notes - Inorganic chemistry" has contents: Chemistry of nonmetals, chemistry of non-transition metals, chemistry of transition metals, lanthanides and actinides, environmental, biological and industrial aspects. | SECTION E—CHEMISTRY IN SOLUTION 147 Fig. 2. Frost diagram for Mn at pH=0 (solid line) and pH=14 (dashed line). The equilibrium constant of this reaction can be calculated by noting that it is made up from the half reactions for MnO2/Mn3+ and Mn3+/Mn2+ each with n=1, and has from Fig. 1. giving K=2×109. The V and MnVI are similarly unstable to disproportionation at pH=0, whereas at pH=14, also shown in Fig. 2. states Mn only MnV will disproportionate. Latimer and Frost diagrams display the same information but in a different way. When interpreting electrode potential data, either in numerical or graphical form, it is important to remember that a single potential in isolation has no meaning, Kinetic limitations Electrode potentials are thermodynamic quantities and show nothing about how fast a redox reaction can take place (see Topic B3). Simple electron transfer reactions (as in Mn3+/Mn2+) are expected to be rapid, but redox reactions where covalent bonds are made or broken may be much slower (see Topics F9 and H7). For example, the potential is well above that for the oxidation of water (see O2/H2O in Table 1), but the predicted reaction happens very slowly and aqueous permanganate is commonly used as an oxidizing agent (although it should always be standardized before use in volumetric analysis). Kinetic problems can also affect redox reactions at electrodes when covalent substances are involved. For example, a practical hydrogen electrode uses specially prepared platinum with a high surface area to act as a catalyst for the dissociation of dihydrogen into atoms (see Topic J5). On other metals a high overpotential may be experienced, as a cell potential considerably larger than the equilibrium value is necessary for a reaction to occur at an appreciable rate. Section F— Chemistry of nonmetals F1 INTRODUCTION TO NONMETALS Key Notes Covalent chemistry Ionic chemistry Acid-base chemistry Redox chemistry Related topics Hydrogen and boron stand out in their