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CBSE Class 12-science Answered

The half life for a first order reaction is 60 mins .What percentage of reactant will be left behind after 120mins. 
Asked by ranisantosh117 | 09 Aug, 2018, 12:19: AM
answered-by-expert Expert Answer
Given:
 
 
 
straight t subscript bevelled 1 half end subscript space equals space 60 space min Order space of space reaction space equals space first space order So comma space for space first space order space reaction comma space we space have straight t subscript bevelled 1 half end subscript space equals space fraction numerator 0.693 over denominator straight k end fraction straight k equals space fraction numerator 0.693 over denominator straight t subscript bevelled 1 half end subscript end fraction space space equals fraction numerator 0.693 over denominator 60 end fraction straight k space equals space 0.0115 space straight s to the power of negative 1 end exponent For space time space 120 space min straight k space equals fraction numerator 2.303 over denominator straight t end fraction log fraction numerator open square brackets straight a subscript 0 close square brackets over denominator open square brackets straight a close square brackets end fraction therefore 0.0115 space equals fraction numerator 2.303 over denominator 120 end fraction log fraction numerator open square brackets straight a subscript 0 close square brackets over denominator open square brackets straight a close square brackets end fraction log fraction numerator open square brackets straight a subscript 0 close square brackets over denominator open square brackets straight a close square brackets end fraction equals space 0.6018 fraction numerator open square brackets straight a subscript 0 close square brackets over denominator open square brackets straight a close square brackets end fraction space equals space antilog space left parenthesis 0.6018 right parenthesis fraction numerator open square brackets straight a subscript 0 close square brackets over denominator open square brackets straight a close square brackets end fraction space equals space 3.99 space space space space space space space space space space space space almost equal to space 4 percent sign space of space the space reactant space left space after space 120 min space fraction numerator open square brackets straight a close square brackets over denominator open square brackets straight a subscript 0 close square brackets end fraction cross times 100 space equals 1 fourth space space space space space space space space space space space space space space space space space space space equals 25 percent sign
 
25% reactant will be left behind after 120 min.

Answered by Varsha | 09 Aug, 2018, 12:17: PM

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