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Question
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?
Solution
For first order reaction,
a = 5 g; (a – x) = 3 g; k = 1.15 × 10−3 s−1
t = `2.303/"k" log "a"/(("a" - "x"))`
= `2.303/(1.15 xx 10^-3 "s"^-1) log (5 "g")/(3 "g")`
= `2.303/(1.15 xx 10^-3 "s"^-1) (log 5 - log 3)`
= `2.303/(1.15 xx 10^-3 "s"^-1) (0.6990 - 0.4771)`
= `2.303/(1.15 xx 10^-3 "s"^-1) xx 0.2219`
= 444 S
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