Half life First order reaction

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samera12

@samera12

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8

Posted: 15 years ago

#1

Hi, I was wondering if anyone could help me out with this question. I cant seem to get the answer right.

The first-order reaction has a half-life of 144 min. How long will it take for a sample of acctoacctic acid to be 65% decomposed?

Answer is : 218min

Thanks
samera

Edited by samera143 - 15 years ago

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akhl

@akhl

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24

Posted: 15 years ago

#2

Let initial amount = No

Amount after the decomposition = N

There is 65% decomposition. Therefore 100-65 = 35 % remains

N = 35% of No

Or N = 0.35 No

t = (1/lambda) * ln(No/N)

But lambda = 0.693/T1/2

Therefore t = (T1/2 / 0.693) * ln (No/N)

t = (144 / 0.693) * ln(1/0.35)

t = 218 min

Ans: 218 min

Let me know if you need any further clarification.

Tips:

For first order reaction, remeber the following formulas:-

N = No * e^(-lambda * t)

lambda = 0.693 / (t1/2)

t = (1/lambda) * ln(No/N)

Here No = initial amount

N = amount after time t

lambda = rate constant

t1/2 = half life i.e. the time after which N = half of No

Edited by akhl - 15 years ago

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samera12

@samera12

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Posted: 15 years ago

#3

Thankss alottttt!! Its well explained..😊

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akhl

@akhl

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Posted: 15 years ago

#4

Glad to be of help. Let me know if you need any further help in Physics, Chemistry, Mathematics,

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