CHEMICAL KINETICS QUIZ-3

Q1. Effective collisions are those in which molecules must:

•  Have energy equal to or greater than the threshold energy
•  Have proper orientation
•  Acquire the energy of activation
•  All of the above

Solution
These are the characteristics of effective collisions

Q2.Which of the following theory is not related to chemical kinetics?

•  Collision theory
•  VSPER theory
•  Activated complex theory
•  Absolute reaction rate theory

Solution
VSEPR theory is for bonding concept

Q3.  What is the order of a reaction which has a rate expression rate =k[A]^(3/2) [B]^(-1)?

•   3/2
•  Zero
•  None of these
•  1/2

Solution
C

Q4. Among the following reaction, the fastest one is:

•  Burning of coal
•  Rusting of iron in moist air
•  Conversion of monoclinic sulphur to rhombic sulphur
•  Precipitation of silver chloride by mixing silver nitrate and sodium chloride solutions

Solution
Ionic reactions are instantaneous

Q5.In a chemical reaction two reactants take part. The rate of reaction is directly proportion to the concentration of one of them and inversely proportional to the concentration of the other. The order of reaction is

•  0
•  1
•  2
•  4

Solution
 The order of reaction is zero. Suppose the following reaction take place . A+B→product ∴rate=[A] [B]^(-1) ∴ order =1+(-1)=0

Q6. At 373 K, a gaseous reaction A→2B+C is found to be of first order. Starting with pure A, the total pressure at the end of 10 min was 176 mm and after a long time when A was completely dissociated, it was 270 mm. The pressure of A at the end of 10 min was

•  94 mm
•  47 mm
• 43 mm
•  90 mm

Solution

Q7.An exothermic chemical reaction occurs in two steps as follows

•  a)
  
  
  
•  b)
  
  
  
•  c)
  
  
  
•  All are correct

Solution
The reaction occurring in two steps has two activation energy peaks. The first step, being fast needs less activation energy. The second step being slow, needs more activation energy. Therefore, second peak will be higher than the first

Q8.The activation energy of a reaction at a given temperature is found to be 2.303RT J mol^(-1) . The ratio of rate constant to the Arrhenius factor is

•  0.01
•  0.1
•  0.02
•  0.001

Solution
Arrhenius equation is, Rate constant, k=Ae^(-E_a |RT) k=Ae^(-2.303 RT/RT) k/A=e^(-2.303) On solving, we get k/A=〖10〗^(-1)

Q9.The unit of rate constant of second order reaction is

•  Mol/Ls
•  L^2/ mol^2
•  Per second
•  L / Mol s

Solution
The units of the rate constant for nth order reaction is (mol/L)^(1-n) s^(-1) ∴ for second order reaction, Unit of rate constant(mol/L)^(1-n) s^(-1) mol^(-1) Ls^(-1)=L /mol-s

Q10. Consider a reaction; aG+bH→Products When concentration of both the reactants G and H is doubled, the rate increases by eight times. However, when concentration of G is doubled keeping the concentration of H fixed, the rate is doubled. The overall of the reaction,

•  0
•  3
•  1
• 2

Solution
aG+bH→Products Suppose order of reaction =n When concentration of both G and H doubled then rate increases by eight times. rate=k(reactants)^n (8)=k(2)^n (2)^3=k(2)^n n=3 When concentration of G is doubled keeping the concentration of H fixed, the rate is doubled. Rate=[G]^1 then, Rate=[G]^1 [H]^2