Erstellt von Alvaro Vargas Calero
vor mehr als 6 Jahre
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Reaction rate | The speed of a chemical reaction may be defined as the change in concentration of a substance divided by the time interval during which this change is observed |
For a reaction of the form A+B→C , the rate can be expressed in terms of the change in concentration of any of its components | |
in which Δ[A] is the difference between the concentration of A over the time interval t2 – t1: | |
Notice the minus signs in the first two examples above. The concentration of a reactant always decreases with time, so Δ[A] and Δ[A] are both negative. | Since negative rates do not make much sense, rates expressed in terms of a reactant concentration are always preceded by a minus sign to make the rate come out positive. |
Consider now a reaction in which the coefficients are different: | t is clear that [B] decreases three times as rapidly as [A] , so in order to avoid ambiguity when expressing the rate in terms of different components, it is customary to divide each change in concentration by the appropriate coefficient: |
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