250+ TOP MCQs on Kinetics, Mechanism and Thermodynamics and Answers

Unit Processes Multiple Choice Questions on “Kinetics, mechanism and thermodynamics”.

1. Which of the following aromatic sulfonation is not an electrophilic substitution reaction?
a) Nitration
b) Halogenation
c) Alkylation
d) None of the mentioned
Answer: d
Clarification: Aromatic sulfonation, like nitration, halogenation, alkylation, and acylation, is a typical electrophilic substitution reaction.

2. How does Sulfonation differ from other reactions?
a) Reaction temperature
b) Reversible reaction
c) Both temperature and reversible reaction
d) None of the mentioned
Answer: c
Clarification: Sulfonation, differs from these other reactions in two marked respects: it is reversible, and reaction temperature can, in certain cases, have an important influence on the position of the entering group.

3. When H₂SO₄ is used as a Sulfonating agent, what effect does formation of water has on the reaction?
a) Slows down the reaction
b) Fast the reaction
c) Reduces activation energy
d) None of the mentioned
Answer: a
Clarification: When sulfuric acid is used as the sulfonating agent, the formation of water slows the reaction to such degree that rate studies can often be made only during the initial stages, rate of sulfonation is inversely proportional to the square of the water concentration.

4. Which of the following is a true Sulfonating agent?
a) SO₃
b) H₃SO₄+
c) HSO₃+
d) All of the mentioned
Answer: d
Clarification: In an aqueous sulfuric acid as many as four different reactive species have been proposed as the true sulfonating agent: (1) H₂SO₄+, (2) SO₃ or a solvate, (3) H₈₀a+ or a solvate, and (4) S₂O₆ (dimeric SO₃).

5. Aromatic substitution reactions, including sulfonation, are conceived in two steps.
a) True
b) False
Answer: a
Clarification: Aromatic substitution reactions, including sulfonation, are conceived as proceeding in two steps, the first involving reagent attack and the second proton removal.

6. Why is the intermediate compound in Sulfonation electrically more stable ?
a) It contains negative charge
b) It contains positive charge
c) It’s neutral
d) None of the mentioned
Answer: a
Clarification: The intermediate compound above is electrically neutral and, therefore, more stable than the analogous intermediates involved in nitration and halogenation, which bear positive charges.

7. Complete the following reaction: ROH + H₂SO₄ _______ + H₂O.
a) RSO₂H
b) RSO₃H
c) ROSO₃H
d) None of the mentioned
Answer: c
Clarification: The reaction is as follows: ROH + H₂SO₄ ROSO₃H + H₂O.

8. Which type of reaction is the heat of Sulfonation reaction?
a) Exothermic
b) Endothermic
c) Neutral
d) None of the mentioned
Answer: a
Clarification: The heat of sulfonation with SO₃ vapour which is dHv is an exothermic reaction.

9. What is (dH)D ?
a) Heat of Sulfonation
b) Heat of Dissociation
c) Heat of Deformation
d) Heat of Formation
Answer: b
Clarification: “(dH)D” is called Heat of Dissociation of Sulfonating agents into SO₃ vapor and compound reagent.

10. What do we denote Heat of Sulfonation with SO₃ vapour as?
a) dHv
b) dHD
c) dHc
d) dHf
Answer: a
Clarification: dHv is called Heat of sulfonation with vapour SO₃ which is an exothermic reaction.