Calculate the half life of a first order reaction from their rate constants given below:

(i) 200 s^{-1} (ii) 2 min^{-1} (iii) 4 years^{-1}

Half life of first order reaction is, t_{1/2} = ln2/K where t_{1/2} is half life of first order reaction, K is rate constant of First order reaction.

(i) t_{1/2} = ln2/200 s^{-1}

⇒ t_{1/2} = 0.693/200 s^{-1} (∵ ln2 = 0.693)

⇒ t_{1/2} = 0.003465 sec.

(ii) t_{1/2} = ln2/2 min^{-1}

⇒ t_{1/2} = 0.693/2 min^{-1} (∵ ln2 = 0.693)

⇒ t_{1/2} = 0.3465 min

(iii) t_{1/2} = ln2/4 year^{-1}

⇒ t_{1/2} = 0.693/4 years ^{-1} (∵ ln2 = 0.693)

⇒ t_{1/2} = 0.17325 year.

__Half life of 3 reactions are 0.003465 sec, 0.3465 min, 0.17325 year respectively.__

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