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Cool goIITian

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20 Jun 2008 23:36:12 IST

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Chemical Kinetics Problems

None

Q1) The activation energy of the reaction: 2HI (g) --------> H₂ + I₂ is 209.5 KJ/mol. Calculate the fraction of molecules of reactants having energy equal to or greater than activation energy.

Q2) The half life for radioactive decay of ¹⁴C C is 5730 years. A sample had 80% ¹⁴C . Estimate the age of the sample.

Q3)The rate constant for the decomposition of hydrocarbons is 2.418 * 10^-5 at 546 K. If the energy of activation is 179.9 kJ/mol, what is the value of pre-exponential factor.

Q4)The decomposition of A into product has value of k as 4.5 * 10³ /s at 10 degrees celsius and energy of activation 60 kJ/mol. At what temperature would k be 1.5 8 10⁴ /s.

pls explain

thnx

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Comments (5)

Rohan

Blazing goIITian

Joined: 3 Jun 2007

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20 Jun 2008 23:56:32 IST

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q1---

fraction of molecules of reactants having energy equal to or greater than activation energy= e^(-E/RT)

put the values n get the answer

q3---

k=Ae^(-E/RT)

k=2.418 * 10^-5

E=179.9 kJ/mol

T=546 K

R=0.0821

now put these values and get the value of A

hope it helps...

MUDIT

Blazing goIITian

Joined: 19 May 2007

Posts: 353

20 Jun 2008 23:57:56 IST

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for the second one. the decay constant of the reaction is ln2/T
where T is the half life of the reaction = 5730 years
so letAo be the initial conc of carbon in the sample and At be the final so At = 0.8Ao and so usin that formula
ln(Ao/0.8Ao)=(ln2/5730)t
and so t comes out to be round abt 1910 years
please correct me if i am wrong or nudge me if you have any doubts

aNdRoMeDa

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21 Jun 2008 00:04:48 IST

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fpr d last one

log (k2/k1)=Ea/(2.303R)*(T2 - T1/t2*t1)

here substitue k1 as d given value

and k2 we wanna find hope it helps

MUDIT

Blazing goIITian

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Posts: 353

21 Jun 2008 00:09:46 IST

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4 pretty same asw the third one

use the equation k=Ae^-E/RT

so for the process occurin at different temperature energy of activation will remain the same

k1=Ae^-E/RT1

k2=Ae^-E/RT2

so k1/k2=e^(E/R)(1/T2-1/T1)

so let k1=4.5*10^3

T1=283K

k2=1.5*10^4

T2=?

E=60kJ/mol=60000J/mol

solve and calculate the ans

it is a little lengthy calculation but if you have any doubts then please feel free to ask

MUDIT

Blazing goIITian

Joined: 19 May 2007

Posts: 353

21 Jun 2008 00:19:31 IST

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ans to 4th one comes to 297.62K or 24.62C

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