Define average rate of a reaction.

Explanation

Average rate of a reaction : The average rate of a reaction during a finite time interval is called average rate of a reaction :
Instantaneous rate of a reaction : The rate of a chemical reaction determined at a specific time is called instantaneous rate of reaction.
For the reaction
`R rarr P`
Average rate of reaction= `-(Delta[R])/(Deltat)=(Delta[P])/(Deltat)`
Instantaneous rate of reaction = `-(d[R])/(dt)=(d[P])/(dt)`