Question

A reduction in concentration of A from 120 mg/L to 2
mg/L in two hours. It is a zero order reaction determine the value of
the rate constant with appropriate units. Repeat the analysis if the reaction is known to follow first-order kinetics.

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Answer 1

Initial concentration = 120 mg/L

Final concentration = 2 mg/L

Time = 2 hr

For the zero order reaction :-

$A= \left [ A_{0} \right ]-k.t$

putting the values we get

$2 mg/L= 120mg/L-k\times 2 hr$

For the first order reaction the formula is:-

$ln\left [ A \right ]=-k.t +ln\left [ A_{0} \right ]$

putting values we get:-

$ln\left [ 2\right ]=-k\times 2 hr +ln\left [ 120 \right ]$

$0.693=-k\times 2 hr +4.787$