Question

When does the average rate of a reaction becomes equal to instantaneous rate?

Answer 1

When $\Delta tapproaches0$, i.e. when it is infinitesimally small, then average rate of a reaction becomes equal to instantaneous rate.
Mathematically, $\frac{dx}{dt}=\underset{\Delta t\to 0}{lim}\frac{\Delta x}{\Delta t}$

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