JEE Advanced levelSingle correct optionDifficulty 3 of 3ck045
A first order reaction has [A]=0.54M at t=10min and [A]=0.18M at t=30min. The initial concentration is
A1.62M
B0.94M
C0.72M
D1.08M
Answer: B
Over the 20 min between the two readings the concentration falls by a factor 3, so k=ln3/20=0.0549min−1. Going back 10 min multiplies [A] by e10k=31/2=1.732. Therefore [A]0=0.54×1.732=0.94M.