A first order reaction has a rate constant of `1.15 xx 10^(-3) s^(-1)` How long will 5 g of this reactant take to reduce to 3g?

Explanation

For a first order reaction,
` k=( 2.303 )/(t) log "" (a)/( a-x)`
here ` a=5 , (a-x) =3 g , k = 1.15 xx 10^(-3) s^(-1)`
Substituting the values,
` t=( 2.303 )/( 1.15 xx 10^(-3)) log "" 5/3 = 2.002 xx 10^(-3) ( log 5- log 3)`
`= 2.002 xx 10^(-3) [0.6989 - 0.4771 ]=444 s`