1. Choose the most correct option.
i. The rate law for the reaction aA + bB P is rate = k[A] [B]. The rate of reaction doubles if
a. concentrations of A and B are both doubled.
b. [A] is doubled and [B] is kept constant
c. [B] is doubled and [A] is halved
d. [A] is kept constant and [B] is halved.
ii. The order of the reaction for which the units of rate constant are mol dm-3 s-1 is
a. 1
b. 3
c. 0
d. 2
iii. The rate constant for the reaction 2 N2O5(g) 2 N2O4(g) + O2(g) is
4.98 × 10-4 s-1. The order of reaction is
a. 2
b. 1
c. 0
d. 3
iv. Time required for 90 % completion of a certain first order reaction is t. The time required for 99.9 % completion will be
a. t
b. 2t
c. t/2
d. 3t
v. Slope of the graph ln[A]t versus t for first order reaction is
a. -k
b. k
c. k/2.303
d. -k/2.303
vi. What is the half life of a first order reaction if time required to decrease concentration of reactant from 0.8 M to 0.2 M is 12 h?
a. 12 h
b. 3 h
c. 1.5 h
d. 6 h
vii. The reaction, 3 ClO ClO3 +2 Cl occurs in two steps,
(i) 2 ClO- ClO2
(ii) ClO2 + ClO ClO3 + Cl The reaction intermediate is
a. Cl
b. ClO2
c. ClO3
d. ClO
viii. The elementary reaction
O3(g) + O(g) 2 O2(g) is
a. unimolecular and second order
b. bimolecular and first order
c. bimolecular and second order
d. unimolecular and first order
ix. Rate law for the reaction, 2 NO + Cl2 2 NOCl is rate = k[NO2]2[Cl2]. Thus k would increase with
a. increase of temperature
b. increase of concentration of NO
c. increase of concentration of Cl2
d. increase of concentrations of
both Cl2 and NO
x. For an endothermic reaction, X Y. If Ef is activation energy of the forward reaction and Er that for reverse reaction, which of the following is correct?
a. Ef = Er
b. Ef < Er
c. Ef > Er
d. ΔH = Ef – Er is negative
2. Answer the following in one or two sentences
i. For the reaction, N2(g) + 3 H2(g) 2 NH3(g),
what is the relationship among d[N2] /dt , d[H2] /dt and d[NH3] /dt ?
ii. For the reaction, CH3Br(aq) + OH-(aq) CH3OH (aq) +Br (aq), rate law is rate = k[CH3Br][OH ] a. How does reaction rate changes if [OH ] is decreased by a factor of 5 ? b. What is change in rate if concentrations of both reactants are doubled?
iii. What is the relationship between coefficients of reactants in a balanced equation for an overall reaction and exponents in rate law. In what case the coefficients are the exponents?
iv. Why all collisions between reactant molecules do not lead to a chemical reaction?
v. What is the activation energy of a reaction?
vi. What are the units for rate constants for zero order and second order reactions if time is expressed in seconds and concentration of reactants in mol/L?
vii. Write Arrhenius equation and explain the terms involved in it.
viii. What is the rate determining step?
ix. Write the relationships between rate constant and half life of first order and zeroth order reactions.
x. How do half lives of the first order and zero order reactions change with initial concentration of reactants?
3. Answer the following in brief.
i. How instantaneous rate of reaction is determined?
ii. Distinguish between order and molecularity of a reaction.
iii. A reaction takes place in two steps, 1. NO(g) + Cl2(g) NOCl2(g)
2. NOCl2(g) + NO(g) 2 NOCl(g)
a. Write the overall reaction. b. Identify reaction intermediate. c. What is the molecularity of each step?
iv. Obtain the relationship between the rate constant and half life of a first order reaction
v. How will you represent zeroth order reaction graphically?
vi. What are pseudo-first order reactions? Give one example and explain why it is pseudo-first order.
vii. What are requirements for the colliding reactant molecules to lead to products?
viii. How catalyst increases the rate of reaction? Explain with the help of potential energy diagram for catalyzed and uncatalyzed reactions.
ix. Explain with the help of Arrhenius equation, how does the rate of reaction changes with (a) temperature and (b) activation energy.
x. Derive the integrated rate law for first order reaction.
xi. How will you represent first order reactions graphically
xii. Derive the integrated rate law for the first order reaction, A(g) B(g) + C(g) in terms of pressure
xiii. What is zeroth order reaction? Derive its integrated rate law. What are the units of rate constant?
xiv. How will you determine activation energy: (a) graphically using Arrhenius equation (b) from rate constants at two different temperatures?
xv. Explain graphically the effect of temperature on the rate of reaction.
xvi. Explain graphically the effect of catalyst on the rate of reaction.
xvii. For the reaction 2A + B products ,find the rate law from the following data.
4. Solve
i. In a first order reaction, the concentration of reactant decreases from 20 mmol dm-3 to 8 mmol dm-3 in 38 minutes. What is the half life of reaction? (28.7 min)
ii. The half life of a first order reaction is 1.7 hours. How long will it take for 20% of the reactant to react? (32.9 min)
iii. The energy of activation for a first order reaction is 104 kJ/mol. The rate constant at 25 0C is 3.7 × 10-5 s-1. What is the rate constant at 300C? (R = 8.314 J/K mol) (7.4 × 10-5)
iv. What is the energy of activation of a reaction whose rate constant doubles when the temperature changes from 303 K to 313 K? (54.66 kJ/mol)
v. The rate constant of a reaction at 5000C is 1.6 × 103 M-1s-1. What is the frequency factor of the reaction if its activation energy is 56 kJ/mol. (9.72 × 106 M-1s-1)
vi. Show that time required for 99.9% completion of a first order reaction is three times the time required for 90% completion.
vii. A first order reaction takes 40 minutes for 30% decomposition. Calculate its half life. (77.66 min)
viii. The rate constant for the first order reaction is given by log10 k = 14.34 – 1.25 × 104 T. Calculate activation energy of the reaction. (239.3 kJ/mol)
ix. What fraction of molecules in a gas at 300 K collide with an energy equal to activation energy of 50 kJ/mol ? (2 × 10-9)