Question

A $\rightarrow$ P is a first-order reaction. The change in concentration of A with time is shown below. The instantaneous rate at points X, Y and Z is \( R_X \), \( R_Y \), and \( R_Z \), respectively. What is the correct order of \( R_X \), \( R_Y \), and \( R_Z \)?

• A. \( R_Y>R_X>R_Z \)
• B. \( R_Y>R_Z>R_X \)
• C. \( R_X>R_Y>R_Z \)
• D. \( R_Z>R_X>R_Y \)

Hint:

In a first-order reaction, the rate is directly proportional to the concentration of the reactant. Higher concentration results in a higher reaction rate.

Answer 1

The Correct Option is A

Step 1:
For a first-order reaction, the rate of the reaction is directly proportional to the concentration of reactant. Thus, the rate at a given point is highest when the concentration of the reactant is highest.
Step 2:
From the graph, it is clear that the concentration of A is highest at point Y, followed by point X, and lowest at point Z.
Step 3:
The rate is proportional to the concentration of A, so: \[ R_Y>R_X>R_Z \] Thus, the correct order is \( R_Y>R_X>R_Z \).