1.

A first orderreactionhasa specific reaction rate of 10^(-2) S^(-1). How much timewill it take for 20 gof thereactanttoreduceto 5 g?

Answer»

238.6s
138.6s
346.5s
693.0s

Solution :for a first orderreaction
rate constant`(K) =(2303)/(t) log (a) /(a-x)`
wherea initial CONCENTRATION
`a-x=`concentration after time't'
.t= timein sec
given a=20 g,a-x =5g.k =`10^(-2)`
`thereforet=(2303)/(10^(-2))log (20)/(5) `
`=1386s`
ALTERNATIVELY ,
Half - lifeforthefirstorderreaction
`(t_(1//2))/(2)=(0.693)/(10^(-2))=69.3 s`
twohalf -livesarerequiredfor thereductionof 20 g of REACTANT into5g
`20 g OVERSET( t_(1//2)) to 10g overset( t_(1//2))to 5g.`
`therefore"totaltime "=2t_(1//2)=2xx69.3=138.6s`


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