(ii)
(b) The thermal decomposition of HCOOH is a first order
reaction with a rate constant of 
at a
certain temperature. Calculate how long will it take for three-fourths of
initial quantity of HCOOH to decompose (log 0.25
=-0.6021). [2+3]
Or
(a) For the reaction, 
the
rate 
with 
.
Calculate the initial rate of reaction when 
Calculate
the rate of reaction after [A] is reduced to 0.06 
.
(b) The rate constant for the decomposition of
hydrocarbons is 
at
546 K. If the energy of activation is 179.9 kJ mol"1 what will
be the value of pre exponential
factor? [2 + 3]
Answer:
(a) For a
reaction 
Product,
rate law is the expression for the rate in terms of molar concentration of the
reactants
where k
is called rate constant.
x is the
order of the reaction wrt A.
y is
the order of the reaction wrt B.
If 
then
Thus rate
constant is the rate of the reaction at a time when molar concentration of each
reactant is 
[1]
Unit of k
is 
If order =
n (i)
Thus, (1-n) =
1
n = 0 order
= zero 
(ii)
Thus,
1-n=-1
Thus,
n=2
Order =
2
(b) 
If a =1
[1]
Alternate
(short) method We know (75
(time of 75%
reaction) 
For first
order reaction 
[1]
Or
(a)
[1]
0.1
0.2
At time t 
[1]
(b)
[1]
[1]
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