JEE Main202623 January 2026Evening ShiftChemistryChemical KineticsActual
Observe the following reactions at T ( K ) . I. A products. II. 5 Br ⁻( aq )+ BrO ₃ ⁻( aq )+6 H ⁺( aq ) 3 Br ₂( aq )+3 H ₂ O ( l ) Both the reactions are started at 10.00 am. The rates of these reactions at 10.10 am are same. The value of - [ Br ⁻ ] t at 10.10 am is 2 10⁻⁴ ~mol ~L ⁻¹ ~min ⁻¹ . The concentration of A at 10.10 am is 10⁻² ~mol ~L ⁻¹ . What is the first order rate constant (in min ⁻¹ ) of reaction I ?
Options
- A10⁻²
- B10⁻³
- C2 10⁻³
- D4 10⁻³
Correct answer
D. 4 10⁻³
Step-by-step solution
For reaction II: 5Br ^- + BrO₃^- + 6H ^+ 3 Br₂ + 3 H₂ O, The overall reaction rate is: r = - 1 5 [Br^-] t = - 1 3 [Br₂] t . Given [Br^-] t = 2 10⁻⁴ mol L ⁻¹ min ⁻¹ The reaction rate is r = 2 10⁻⁴ 5 = 4 10⁻⁵ mol L ⁻¹ min ⁻¹ . Since the rates of both reactions are equal at 10.10 am and reaction I is first-order: r = k[A] , so 4 10⁻⁵ = k 10⁻² , giving k = 4 10⁻³ min ⁻¹ .