* Chemical reactions are thermodynamically "favorable" if the overall energy the the products is lower than the overall energy of the reactants. The formation of products, however, first requires bond breakage in the reactants, and the energy required to break them represents an energy barrier known as the "activation energy," or Ea. Measuring Activation Energy
* The determination of activation energy requires kinetic data, i.e., the rate constant, k, of the reaction determined at a variety of temperatures. The student then constructs a graph of ln k on the y-axis and 1/T on the x-axis, where T is the temperature in Kelvin. The data points should fall along a straight line, the slope of which is equal to (-Ea/R), where R is the ideal gas constant. Iodine-Clock Activation Energy
* The plot of (ln k) vs. (1/T) for the iodine clock reaction should reveal a slope of about -6230. Thus, (-Ea/R) = -6230. Using an ideal gas constant of R = 8.314 J/K.mol gives Ea = 6800 * 8.314 = 51,800 J/mol, or 51.8 kJ/mol.
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