JEE Main 2021 · 26 August · morning · Numerical answer · +4 / −0
The following data was obtained for chemical reaction given below at 975 K.
2NO (g) + 2H 2(g) → N 2(g) + 2H₂O (g)
The order of the reaction with respect to NO is ___________. [Integer answer]
Answer and solution
Answer 1
Solution
Chemistry ma’am · 3 steps
Pick the two runs where only [NO] changes, then see how many times the rate changes.
- Choose the runs. In runs A and B, [H₂] stays at 8 × 10⁻⁵ mol L⁻¹. Only [NO] changes, so any change in rate comes from NO alone.
- Compare the ratios. [NO] goes from 8 × 10⁻⁵ to 24 × 10⁻⁵, which is 3 times. The rate goes from 7 × 10⁻⁹ to 2.1 × 10⁻⁸, which is also 3 times.
Rate_B/Rate_A = ([NO]_B/[NO]_A)ˣ ⇒ 3 = 3ˣ ⇒ x = 1
- So. The order with respect to NO is 1. Runs B and C show the order in H₂ is also 1, since 4 times the [H₂] gives 4 times the rate.
The common slip: 2. Taking the order from the coefficient of NO in the balanced equation gives 2, not 1. The data shows the rate only triples when [NO] triples.
The idea to keep. Order comes from experiment, never from the balanced equation. Hold every other concentration fixed and match the rate ratio to the concentration ratio raised to the order.
Answer from the NTA final answer key. Solution by PrepWiser.