Q 1 :    

NO2 required for a reaction is produced by decomposition of N2O5 in CCl4 as by equation

2N2O5(g)4NO2(g)+O2(g)

The initial concentration of N2O5 is 3 mol L-1 and it is 2.75 mol L-1 after 30 minutes.

The rate of formation of NO2 is x×10-3 mol L-1 min-1, Value of x is ________ . (nearest integer)              [2024]



(17)

                  Rate of dissociation of N2O5:  -Δ[N2O5]t=-(2.75-3)mol L-130min=1120molL min

                  By stoichiometry of the reaction, 2N2O5(g)4NO2(g)+O2(g)

                  Rate of reaction=-12Δ[N2O5]t=14Δ[NO2]t

                  Δ[NO2]t=2×Δ[N2O5]t

                  Δ[NO2]t=2×1120molL min=16.67×10-3molL min17×10-3molL min

 



Q 2 :    

Consider the following single step reaction in gas phase at constant temperature.

2A(g)+B(g)C(g) 

The initial rate of the reaction is recorded as r1 when the reaction starts with 1.5 atm pressure of A and 0.7 atm pressure of B. After some time, the rate r2 is recorded when the pressure of C becomes 0.5 atm. The ratio r1:r2 is _________ ×10-1. (Nearest Integer)               [2024]



(315)

                                   2A(g)          +           B(g)               C(g)

                      t = 0      1.5 atm                     0.7 atm

                    (press)

                      t = t      (1.5 - 2p) atm         (0.7 - p) atm               p atm

                    (press)

                    Since reaction is single step reaction, its rate law can be written from stoichiometry of the reaction as:

                    r=k(PA)2(PB)

                   Initial rate r1 is thus r1 = k(1.5)2(0.7)

                   As given in question p = 0.5 atm

                   Thus pressure of A after sometime

                                =(1.5-2p)atm=(1.5-2×0.5)atm=0.5atm

                   Pressure of B after sometime

                                =(0.7-p)atm=(0.7-0.5)atm=0.2atm

                  Rate after sometime, r2=k(0.5)2(0.2)

                   r1r2=k(1.5)2(0.7)k(0.5)2(0.2)=315×10-1

                    

 



Q 3 :    

Consider the following first order gas phase reaction at constant temperature

A(g)2B(g)+C(g)

If the total pressure of the gases is found to be 200 torr after 23 sec. and 300 torr upon the complete decomposition of A after a very long time, then the rate constant of the given reaction is ______ ×10-2s-1 (nearest integer).    

[Given: log10(2)=0.301]                   [2024]



(3)

                                     A(g)                    2B(g)        +         C(g)

                       t = 0       Po                               0                           0

                       (press.)

                       t = 23 s    Po-P                    2P                        P      Total=Po+2P=200   ...(i)

                       (press.)

                       t =          0                           2Po                     Po       Total=3Po=300    ...(ii)

                       (press.)

                             From (i) and (ii)

                       Po=100 torr, P=50 torr

                       For first order reaction, rate constant k is given as:

                       k=2.303tlog10PoPo-P

                      k=2.30323log10100100-50

                      k=2.30323log102s-1=2.30323×0.301s-1=0.0301s-13×10-2s-1

                       

 



Q 4 :    

Consider an elementary reaction A(g) + B(g) → C(g) + D(g)

If the volume of reaction mixture is suddenly reduced to 13 of its initial volume, the reaction rate will become ‘x’ times of the original reaction rate. The value of x is:     [2025]

  • 13

     

  • 19

     

  • 3

     

  • 9

     

(4)

A(g) + B(g) → C(g) + D(g)

Since it is an elementary reaction, r = k[A][B]. i.e. it is a second order reaction. Reducing volume three times increases concentration of both A and B three times. So rate of reaction becomes 3 × 3 = 9 times.

 



Q 5 :    

Rate law for a reaction between A and B is given by R=k[A]n[B]m

If concentration of A is doubled and concentration of B is halved from their initial value, the ratio of new rate of reaction to the initial rate of reaction (r2r1) is      [2025]

  • 2(n-m)  

     

  • (n-m)  

     

  • (m+n)  

     

  • 12m+n

     

(1)

r1=k[A]n[B]m

r2=k[2A]n[B2]m

r2r1=k[2A]n[B2]mk[A]n[B]m 

r2r1=2n-m



Q 6 :    

A(g)B(g)+C(g) is a first order reaction.                     [2025]

Time T
Psystem Pt P

 

The reaction was started with reactant A only.  

Which of the following expression is correct for rate constant k ?

  • k=1tln2(P-Pt)Pt

     

  • k=1tlnPPt

     

  • k=1tlnP2(P-Pt)

     

  • k=1tlnP(P-Pt)

     

(3)

A(g)B(g)+C(g)t=0 (press)Po00t=t (press)Po-pppTotal=Po+p=Pt-It=∞ (press)0PoPoTotal=2Po=P-II

 From I and II:

Po=P2,  p=Pt-P2 

For first order reaction, rate constant k is:

k=2.303tlogPoPo-p 

=2.303tlogP2P2-(Pt-P2) 

=2.303tlogP2(P-Pt)