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Some rate laws depend on the concentration of more than one species. For instance, oxidation of iodide ions by persulfate ions: Rate of consumption I- = k[S2O82-][I-]. In such cases, the analysis can be simplified by ensuring that one species remains at the same _________ during the reaction so it can be used as a ______.
In rate laws that depend on the concentration of more than one species, explain a technique used to keep one of the species constant.
Starting the reaction with one of the species in such a high concentration that their concentration barely changes in the course of the reaction.
In the case of the oxidation of iodide ions by persulfate ions: Rate of consumption I- = k[S2O82-][I-], if we started with so much [S2O82-] that it was practically constant throughout our reaction, what would the rate of consumption of I- be? What is k'? What order of reaction do we have know?
- Rate of consumption of I- = k'[I-]
- k' is the value k[S2O82-], which is another constant
- We have gone from a second order reaction to a pseudo-first order reaction
half life; it is the time needed for the concentration of a substance to fall one-half its initial value
Write an equation that shows the relation between the rate constant and the half-life of a reactant in a first order reaction. It should show that the greater the rate constant, the ______ the half-life of a substance.
t1/2 = ln2/k
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