A first order reaction has a rate constant of 2.303×10-3s-1. The time required for 40 g of this reactant to reduce to 10 g will be  [Given that log102=0.3010

For a first order reactionHalf life period, t12=0.693k=0.6932.303×10−3s−1=300.91s Now, 40g→t1/2 20g→t1/2 10gSo, 40 g substance requires 2 half life periodsto reduce up to 10 g∴ Time taken in reduction = 2 × 300.91 s                                                        =601.82≃602s