Download Extra: A Comparison of Average Rate, Rate Law and Integrated

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A COMPARISON OF RATE CONCEPTS
1. The average rate (unique) expression helps us to relate the rates of appearance/disappearance of the
species present.
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It uses the coefficients of the balanced chemical reaction.
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Generally, average reaction rate for a given time interval can be calculated from the concentrations
of either the reactant or one of the products at the beginning of the interval (time = t0) and at the end
of the interval (t1)
2. The rate law tells us how the rate is related to the concentrations (or pressures) of reactant. The rate law
is essentially a form of instantaneous rate, as it is a measure of the rate of reaction at a specific time.
Thus, a time interval or change in time (Δt) is not part of the rate law, as the rate law represents a single
point in time, when the concentrations are applied to the expression.
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The rate law employs the use of rate orders. A rate order indicates the impact a change in the
molar concentration of that reactant has on the rate (none, proportional, square or cube … or some
fraction).
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The rate law also introduces the rate constant which indicates the fraction of reactant species
moving along a specific pathway
3. The integrated rate law gives you the amount of time (t) it takes to get from an initial concentration of
a reactant to some other concentration.
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The form of the integrated rate law equation depends on the order of the reaction with respect to the
reactant in question.
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The integrated rate law re-introduces time, into a rate equation, but it is blended (integrated) with the
change in concentration of a species. It is a rather powerful tool for determining half-life issues of
radioisotopes, concentrations of pharmaceuticals in a living system over time, or issues such as the
rate of pesticide degradation over time, in an ecosystem.