Question

5. Elementary rate expressions. (Langmuir, pg. 50-60; Section 2.7.5, pg. 71-73) (a) What is the difference between an elementary reaction and an overall reaction in kinetic treatment of chemical reactions? (b) For many complex reactions in natural systems, reaction rates are approximated by a fitting an overall reaction and determining a "pseudo-order" rate expression and rate constant. This treats an overall reaction mathematically the same as an elementary reaction, even though the reaction mechanism does not necessarily apply at the molecular scale. For example, the overall oxidation of Fe to Fe at low pH in air can be written Fe2+ + 0.2 502(aq) + H+ = Fe3+ + 0.5 H2O At low pH, the rate of oxidation is observed to be independent of pH, but this reaction can be slow unless oxidation by 02 is catalyzed by bacteria. Write a rate expression for Fe oxidation at low pH that has a pseudo-first order dependence on the concentration of O2. Briefly explain your expression

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Answer 1