A first order reaction has a rate constatn `1.15 xx10^(-3) s ^(-1).` How long will 5 g of this reactant take to reduce to 3 g ?

Explanation

Rate constant `[k] =1.15xx10^(-3) s^(-1)`
initial amount `[R]_(0)=5g,` Final a amount `[R]=3g`
`t=(2.303)/(R) log ""([R]_(0))/(R)`
`=(2.303)/((1.15xx10^(-3) s^(-1)))log"" ((5g)/(3g))=(2.303)/([1.15xx10^(-3) s^(-1)]) [log 5- log 3]`
`=(2.303)/(1.15xx10^(-3) s^(-1))(0.6990-0.4771)=2.0 xx10^(3)xx 0.2219 s=443.8s`
Time `=444s.`