Rate Constants

[Kennedi2J]

What does it mean for a reaction to be pseudo-first-order?

[Daniel Yu 1E]

A Pseudo First Order Reaction is reaction which is not first-order reaction naturally but made first order by increasing or decreasing the concentration of one or the other reactant is known as Pseudo first order reaction. Pseudo means 'fake'.

[Anuradha S 1F]

To be pseudo-first-order, the concentration of one of the reactants in the rate law must be increased to be much larger than the concentration of the other reactant. For example, look at #15 from ENDGAME. The concentration of A has been increased so much that even when A is used up by the reaction, there is essentially no change in the concentration of A. Because of that, we can say that the rate law of that reaction is only dependent on [B] and is, therefore, pseudo-first-order even though the actual rate law = k[A][B] which is 2nd order.

[Philomena 4F]

To be pseudo-first-order, the concentration of one of the reactants in the rate law must be increased to be much larger than the concentration of the other reactant. For example, look at #15 from ENDGAME. The concentration of A has been increased so much that even when A is used up by the reaction, there is essentially no change in the concentration of A. Because of that, we can say that the rate law of that reaction is only dependent on [B] and is, therefore, pseudo-first-order even though the actual rate law = k[A][B] which is 2nd order.

Is there a guide on how large one [reactant] has to be compared to the other [reactant] for this concept to be applied?