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For the reaction 2NO(g) + O2(g) -> 2NO2(g), doubling [NO] at constant [O2] quadruples the rate, and doubling [O2] at constant [NO] doubles the rate. What is the rate law?
ARate = k[NO][O2]
BRate = k[NO]^2[O2]
CRate = k[NO][O2]^2
DRate = k[NO]^2[O2]^2
Answer & Solution
Correct answer: B. Rate = k[NO]^2[O2]
1. Quadrupling on doubling [NO] means rate $\propto [NO]^2$ (since $2^2=4$).
2. Doubling on doubling [O2] means rate $\propto [O_2]^1$ (since $2^1=2$).
3. Combining, $\text{Rate} = k[NO]^2[O_2]$.
4. Distractor C swaps the two orders; distractor A treats both as first order.
_Source: NCERT Class 12 Chemistry Ch 3 "Chemical Kinetics", p.6_
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