5. Chemical Kinetics

Terms in this set (25)

To use this data, identify a pair of trials in which the concentration of one of the reactants is changed
while the concentrations of all other reactants remain constant. Under these conditions, any change in
the rate of product formation from one trial to the other (if there is any change) is fully attributable to
the change in concentration of that one reactant. Consider a reaction with two reactants, A and B,
forming product C. Imagine two trials in which the concentration of A is constant, while the
concentration of B doubles. If the rate of the formation of product C has subsequently quadrupled,
then the exponent on [B] must be two. Why? Looking at the generic rate law (rate = k[A] [B] ), the
logic should look something like this: Doubling [B] has resulted in a quadrupling of the rate, so to
determine the order of the reaction, y, with respect to B, I need to calculate the exponent to which
the number 2 must be raised to equal 4. Because 2 = 4, y = 2. The next step is to repeat this process for the other reactant, using data from a different pair of trials,
making sure that the concentration of only the reactant we are trying to analyze is changed from one
trial to the other while the concentrations of all other reactants remain the same. Once the orders of
the reaction have been determined with respect to each reactant, we can write the complete rate law,
replacing the exponents x and y with actual numbers. To determine the value of the rate constant k,
plug in actual values from any one of the trials; pick whichever trial has the most arithmetically
convenient numbers.
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