Q126 / 200 · MHT CET - Medical 2026 (23 April Shift 2) · Chemistry
For a reaction, A+B$\rightarrow$Products, that is a second order reaction. Identify the correct rate expression for reaction from the following.
- A$r = K[\text{A}]^2[\text{B}]$
- B$r = K[\text{A}]^{3/2}[\text{B}]$
- C$r = K[\text{A}][\text{B}]^2$
- Correct answerD$r = K[\text{A}][\text{B}]$
Solution
The overall order of a reaction is the sum of the exponents of the concentration terms in the rate law expression.
For the rate expression $r = K[\text{A}]^x[\text{B}]^y$, the overall order is $x + y$.
Checking the given options:
For $r = K[\text{A}]^2[\text{B}]$, order $= 2 + 1 = 3$
For $r = K[\text{A}]^{3/2}[\text{B}]$, order $= 3/2 + 1 = 5/2$
For $r = K[\text{A}][\text{B}]^2$, order $= 1 + 2 = 3$
For $r = K[\text{A}][\text{B}]$, order $= 1 + 1 = 2$
Since the reaction is of second order, the correct rate expression is $r = K[\text{A}][\text{B}]$.
Answer: $r = K[\text{A}][\text{B}]$
For the rate expression $r = K[\text{A}]^x[\text{B}]^y$, the overall order is $x + y$.
Checking the given options:
For $r = K[\text{A}]^2[\text{B}]$, order $= 2 + 1 = 3$
For $r = K[\text{A}]^{3/2}[\text{B}]$, order $= 3/2 + 1 = 5/2$
For $r = K[\text{A}][\text{B}]^2$, order $= 1 + 2 = 3$
For $r = K[\text{A}][\text{B}]$, order $= 1 + 1 = 2$
Since the reaction is of second order, the correct rate expression is $r = K[\text{A}][\text{B}]$.
Answer: $r = K[\text{A}][\text{B}]$
Hence, the correct answer is option: 'D'.