Question

Which of the following do not define instantaneous reaction?
(A) Appearance of a product over a particular time interval.
(B) Change in the concentration of the products at a particular instant of time.
(C) Change in the concentration of the reactants at a particular instant of time.
(D) Reactions completed in a fraction of seconds.

Answer 1

Hint : We know that the term instantaneous rate means the reaction rate at a particular time of very short interval. For determining the instantaneous rate at a definite time t we need to plot the change in rate of the rate of reaction along the x axis and the time interval along the y axis

Complete Step By Step Answer:
The instantaneous rate of reaction is the rate at some instant at a particular time. Specifically it is defined as the change in concentration of the components of a reaction at an infinitely small time interval. The average of the instantaneous reaction rate over a period of time gives the average rate during the reaction. Using the plot we calculate the negative of the slope of the curve of the change in concentration of a reactant with respect to the time at time. It is done by measuring the slope of the tangent to the graph of concentration vs. time.
Thus, Instantaneous rate of reaction measures the infinitesimally small change in concentration that occurs over an infinitesimally short period of time. The rate of reaction changes while it is being measured.
Therefore, correct answer is option A i.e. Appearance of a product over a particular time interval does not define instantaneous reaction.

Note :
Note that the rate of concentration of products increases with time according to the plot seen above and the rate of concentration of reactants decreases with time. Thus a negative slope is obtained in plotting the change in concentration of reactant with time.