Half lives [ENDORSED]
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Blake_Katsev_2E
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Half lives
Why in question 15.35 would you not be able to multiply the half live time by 4 to see how long it takes to get to one 16th its original concentration?
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Chem_Mod
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Re: Half lives [ENDORSED]
The question is for second order reactions, which have the following rate law:
The half life (
) for second order reactions is the following expression:
For second order reactions, the half-life increases over time since there's an inverse relation between concentration and the half-life. As molecules collide and react, the concentration of the molecule decreases which means that the half life will increase. This is in contrary to first-order reactions, in which the half life is given by the following expression:
For first-order reactions, there is no dependence on concentration, only on constants (ln2 and k). Thus, the half life for a first-order reaction is constant whereas the half life for a second order reaction changes over time due to its concentration dependence.
The half life (
For second order reactions, the half-life increases over time since there's an inverse relation between concentration and the half-life. As molecules collide and react, the concentration of the molecule decreases which means that the half life will increase. This is in contrary to first-order reactions, in which the half life is given by the following expression:
For first-order reactions, there is no dependence on concentration, only on constants (ln2 and k). Thus, the half life for a first-order reaction is constant whereas the half life for a second order reaction changes over time due to its concentration dependence.
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