Question

What do you understand by instantaneous rate?

Answer 1

The rate of change of concentration of any of the reactants or products at a particular instant of time is called the instantaneous rate of the given reaction at that instant of time.

Using the standard calculus notation, the instantaneous rate for the reaction \[\ce{A -> B}\] can be expressed as

`"Instantaneous rate" = ("Average rate")_(Delta t -> 0`

or, `"Instantaneous rate" = ((-Delta [A])/(Delta t))_(Delta t -> 0)`

= `((Delta [B])/(Delta t))_(Delta t -> 0)`

or, `"Instantaneous rate" = -(d[A])/(dt)` 

= `(d[B])/(dt)`

where, respectively, d[A] and d[B] stand for small changes in the molar amounts of A and B, and dt stands for an extremely small period of time.