A first order reaction has a rate constant 1.15 × 10-3 s-1. How long will 5 g of this reactant take to reduce to 3 g?
Given-
Rate constant, k = 1.15 × 10-3 s-1
Initial quantity, R0 = 5 g
Final quantity, R = 3 g
According to the formula of first order reaction,
t = 
t = 443.8 s
t = 4.438 × 102 s
The time taken for 5g of the reactant to reduce to 3 g is 4.438 × 102 s
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