13We'll use 0.693/K only, kyunki jab derive kiya hoga, toh tht "2" wud already have been included in "K".
Q. The decomposition of N2O5 is 1st order. 2N2O5 ---> 4NO2 + O2 is 1st order. If the rate constant is
5.90 x 10-4 s-1, what is the half life of this reaction?
will u use t0.5 = 0.693/K
or t0.5 = 0.693/2K
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14 Answers
13
106K of a reaction is constant and doesnot depend on the coefficients...
aisa ek question RCM objectives mein bhi hai...
in that it uses the fact that K is const...
13Yeah, K shud be a constant 'coz tht wud depend upon the rds.
I don' know the mech. of the above reac.n, but if v had-
2N2O -------> 2N2 + O2 (1st Order)
Mech :: N2O ----(slow)-----> N2 + O
N2O + O ---(fast)----> N2 + O2
Toh, depending upon the rds, apan toh yehi likhte naa--- -d(N2O)/dt = K[N2O]
Then integrate karte....
Coeff. kuch bhi hon, par agar 1st order hai toh rds mein coeff. one hi hoga naa....!!
Isliye i think, wo 2 alag se nahi likhenge.
106
see the various solved egs of RCM
use magnifier if not visible
13Hmmm... matlab iske hisaab se v shud consider the coefficients.
Tht means the rds only implies tht the, Rate = (Some const.)* [A]1 ...(V can't say tht "Some const." is "K")
....& in order to keep "K" a particular value fr a particular reac.n, v have to include in the coefficient values.
We are in need of an expert's confirmation here...[12]
1357Basically we should use Kt1/2=ln2
The reaction should not depend on the coefficients as order is practical thing.
Because for first order reactions, we take the rate of disappearance of reactant as the rate of reaction.
so -dN2O5dt=k[N2O5]
24As sir pointed out order of reaction is experimental qty...so it should be independent of coefficents...
becoz if u look at the reaction
2N2O5 ---> 4NO2 + O2
there are not one ,two ....but infinite no. of possible ways to balance the reaction....but that wont mean its order will keep on changing...
13Toh isko, koi finally clear karo..... Is RCM wrong in its solved examples...??
Because such a Qn came in CBSE-2010 too, n i don't think tht they think so deeply or even expect us to think so deeply [3]
106hmm. avik.. in NCERT the rate exp. is also given as in ..RCM
i.e. rate = -12d[N2O5]/dt = 1/4. d[NO2]/dt = d[O2]/dt
but i think we should take rate law exp. as
-d[N2O5]/dt = k[N2O5]