1

12th Agni
Chemical Kinetics DPP-1

1. Draw the graph of the following: 7. Express the rate of the following in terms of
(i) Zero order ammonia.
N2(g) + 3H2(g)  2NH3(g)
(a) Rate vs concentration
(b) t1/2 vs Ro
8. Define activation energy.
(c) R vs t
(ii) Ist order
9. Define rate of reaction. Write two factors that affect
(a) Rate vs Ro the rate of reaction.
(b) T1/2 vs Ro
(c) ln R vs t 10. Give the unit of zero, Ist and IInd order.
R
(d) log o vs t
Rt 11. Distinguish between molecularity and order of a
reaction.
2. What are pseudo first order reactions? Give one
example of such reactions. 12. Explain the difference between the average rate and
instantaneous rate of a chemical reaction.
3. The rate constant of reaction depends on
(1) temperature (2) mass
(3) weight (4) catalyst 13. In a first order reaction, the concentration of the
reactant is reduced from 0.6 mol L–1 to 0.2 mol L–1
4. The addition of a catalyst during a chemical reaction in 5 min. Calculate the rate constant of the reaction.
alters which of the following quantities?
(1) activation energy 14. The decomposition of NH3 on platinum surface is
(2) entropy
zero order reaction. If rate constant (k) is 4 × 10–3
(3) internal energy
(4) enthalpy MS–1, how long will it take to reduce the initial
concentration of NH3 from 0.1 M to 0.064 Μ.
5. The integrated rate law for the reaction H2 + I2 
2HI will be 15. The rate constant for a first order reaction is 60s–1.
d[H2 ] d[I2 ] d[HI] How much time will it take to reduce the initital
(1)  
dt dt dt concentration of the reactant to its 1/10th value?
d[H2 ] d[HI] 1 d[HI]
(2)   16. The decomposition of a compound is found to
dt dt 2 dt
1 d[H2 ] 1 d[I2 ] d[HI] follow a first order rate law. If it takes 15 min for
(3)   20% of original material to react, calculate
2 dt 2 dt dt
d[H 2 ] 1 d[HI] (i) the rate constant.
(4)  
dt 2 dt
17. What is the effect of temperature on the rate constant
6. The threshold energy for a chemical reaction will be.
of a reaction? How can this temperature effect on
(1) activation energy + average energy of
reactants. rate constant be expressed quantitatively?
(2) activation energy - average energy of reactants.
(3) average energy of reactants.
(4) activation energy.
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18. What is arrhenions equation give the graph between 20. A 1st order reaction
log k vs 1/T? k = 693 sec–1
t1/2 = ?
19. The rate of most reactions become double when
their temperature is raised from 298 K to 308 Κ.
Calculate their activation energy.
(Given, R = 8.314J mol–1 K–1)
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Note: Kindly find the Video Solution of DPPs Questions in the DPP Section.

Solution

1. (i) (a)

(d)
(b)
2. Pseudo first order reaction The reaction which is
bimolecular but has order one, is called pseudo first
order reaction, e.g. acidic hydrolysis of ester
H

 CH5COOH  C2H5OH
CH3COOC2H5  H2O 


(c) 3. (1) temperature

4. (1) activation energy

2.(ii) Ist order: d[H 2 ] 1 d[HI]

5. (4)  
dt 2 dt

6. (1) activation energy + average energy of reactants.

7. N2(g) + 3H2(g)  2NH3(g)

d[N2 ] 1 d[H2 ] 1 d[NH3 ]
(a) Rate =  
dt 3 dt 2 dt

8. It is the extra energy contained by reactant molecules

that results into effective collisions between them to
form the products. It is denoted by Ea.

(b)

(c)
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9. (i) Rate of a reaction Change in concentration of [R] [P]

rav   
reactants or products in unit time is known as rate t t
of a reaction. Its unit is (mol L–1)1–n S–1.
Instantaneous rate of reaction It is defined as the rate
(ii) Two factors on which rate of reaction depends
are: of change in concentration of any one of the reactants
(a) Concentration of reactants Generally rate or products at that particular instant of time.
increases with the increase in concentration. For a reaction R → P
(b) Temperature Generally rate of reaction
d[R] d[P]
increases about 2 - 3 times for every 10°C rise rinst   
in dt dt
(dt = very small interval of time)
1n
 Mol  1
10.  lit.  sec
 
Zero = Mol lit–1 sec–1 13. Rate constant,
Ist = sec–1 2.303 [R]o
IInd = Mol–1 lit sec–1 k= log
t [R]

11. Given, [R] = 0.6 mol L–1

Molecularity of reaction Order of reaction
[R] = 0.2 mol L–1, t = 5 min
1. The number of 1. The sum of
reacting species powers of the 2.303 0.6
k log
which must concentrations of 5 0.2
collide the reactants in
2.303
simultaneously in the rate law k log 3
5
order to bring expression is
about a chemical called the order of
reaction is called that chemical
molecularity of a reaction. 14. 2NH3(g)  N2(g) + 3H2(g)
reaction. Given
2. Molecularity is 2. Order may have
k = 4 × 10–3 MS–1
always a whole zero, whole
number value. number, negative [A] = 0.1 M; [A] = 0.064 M
or fractional,
[A0 ]  [A]
values. t=
k
12. Average rate of reaction It is defined as the change in [For zero order reaction]
the concentration of any one of the reactants or prod-
0.1  0.064 0.036 1000
ucts over a long time interval. Average rate of t=   9s
reaction. 4 103 4
Change in concentration
=
Time interval
For a reaction, R  P
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15. For a reaction, 18. k = AeEa /RT

Here, a - x = a / 10
Ea
2.303 a 2.303 a ln k = ln A 
t log  log RT
k ax 60 a / 10
Ea
2.303 log k = log A –
t log 60 2.303RT
60
T = 0.0384 s var% [kaM = ln A

16. (i) First, find the constant by using formula, E a

<ky = 2.303R

log k
2.303 [R]o
k= log
t [R]
Where [R] = a – x and [R]0 = a O
(ii) From the value of k and using the above formula, 1/T
find the value of time at which 10% of the
19. Given T1 = 298 K, T2 = 308 K and k2/k1 = 2 and
original material remains unreacted.
(i) 20% decomposition means [R] = 100, and [R] R = 8.314J mol–1 K–1
100 – 20 = 80. k Ea  T2  T1 
log 2   
2.303 [R]0 2.303 100 k1 2.303R  T1 T2 
k= log = log
t [R] 15 80 Ea  308  298 
log 2  
k=
2.303
 log 1.25 
2.303
 0.0969 2.303  8.314  298  308 
15 15
Ea 10
= 0.0148 min–1 0.3010 = 
2.303  8.314 298  308
17. Rate of reaction increase with temperature. EA = 52903.05 J mol–1
Temperature coefficient is the ratio of rate constant at
temperature (T + 10) K to the rate constant at 0.693 0.693 1103
temperature (1)K. 20. t1/2 =  
k 693 sec
Temperature coefficient

Rate constant at (T+10)K

=
Rate constant at(T)K

It is observed that for a chemical reaction with rise in

temperature by 10°, the rate constant is nearly
doubled.

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