Measuring a second-order reaction rate with reactants `A` and `B` can be problematic: The concentrations of the two reactants must be
followed simultaneously, which is more difficult then to measure one of them and calculate the other as a difference, which is less precise. A common solution for that problem is the pseudo-first-order approximation
If either `[A]` or `[B]` remains constant as the reaction proceeds, then the reaction can be considered pseudo-first-order because, in fact,
it depends on the concentration of only one reactant. If, for example, `[B]` remains constant, then:
`r=k[A][B]=k'[A]`
Where `k' = k[B]_0`, (`k'` or `k_(obs)` with units `s^(-1)`) and an expression is obtained identical to the first order expression above.
One way to obtain a pseudo-first-order reaction is to use a large excess of one of the reactants `([B]`>> `[A])` so that, as the reaction progresses, only a small amount of the reactant is consumed, and its concentration can be considered to stay constant.
Measuring a second-order reaction rate with reactants `A` and `B` can be problematic: The concentrations of the two reactants must be
followed simultaneously, which is more difficult then to measure one of them and calculate the other as a difference, which is less precise. A common solution for that problem is the pseudo-first-order approximation
If either `[A]` or `[B]` remains constant as the reaction proceeds, then the reaction can be considered pseudo-first-order because, in fact,
it depends on the concentration of only one reactant. If, for example, `[B]` remains constant, then:
`r=k[A][B]=k'[A]`
Where `k' = k[B]_0`, (`k'` or `k_(obs)` with units `s^(-1)`) and an expression is obtained identical to the first order expression above.
One way to obtain a pseudo-first-order reaction is to use a large excess of one of the reactants `([B]`>> `[A])` so that, as the reaction progresses, only a small amount of the reactant is consumed, and its concentration can be considered to stay constant.