Verified Solution • 2025–26 Session moderate

QJEEM20Cha60f: JEE Main 2020 Chemistry - Class 12 JEEM20Cha60f Solution: If 75% of a first order reaction was completed in 90 minutes,…

If 75% of a first order reaction was completed in 90 minutes, 60% of the same reaction would be completed in approximately (in minutes) _______.

(Take : log 2 = 0.30; log 2.5 = 0.40)

Step-by-Step Verified Solution

t75% = 90 min = 2 × t1/2

⇒\Rightarrow t1/2 = 45 min

Rate constant, K = 0.69345{{0.693} \over {45}} min-1

Time for completion of 60% of the reaction,

t60% = 2.303Klog⁡104{{2.303} \over K}\log {{10} \over 4}

= 2.303×450.693log⁡2.5{{2.303 \times 45} \over {0.693}}\log 2.5

= 60 min

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