Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

3 THE SOL I D-LI Q U I D I N T ER FA C E 253z is dependent on the rate of stirring, or, in a flow system, on the linear velocityof the fluid. It has also been found that the activation energy is about 4.5 kcal .mole-' in diffusion controlled reactions. The dissolution of metals by iodine/potassium iodide 326 and of iron by hydrochloric have beenshown to be diffusion controlled.Where chemical reaction is the rate determining step, the rate of dissolutionwill be proportional to the surface area and to the concentration of the secondreagentR = KS(C)The rate of dissolution of marble (CaCO,) in hydrochloric acid 328 is an exampleof a chemically controlled reaction. The rate can be measured from the evolutionof carbon dioxide. Palmer and Clark329 found that the rate of dissolution of silicain hydrofluoric acid was proportional to surface area and acid concentration. Therate of reaction was measured by noting the increase in conductivity of the solutionFig. 41. Schematic diagram of ice calorimeter, A, outer jacket; B, cap; C, Dewar vessel; F, tubefor addition of reagents; J, semi-microburette; M, protrusions to hold ice mantle; N, ice mantle.From ref. 332.References pp. 270-278