250+ TOP MCQs on Classification of Reactions and Answers

Chemical Reaction Engineering Multiple Choice Questions & Answers on “Classification of Reactions”.

1. Which of the following represents heterogeneous catalytic reaction?
A. Burning of coal
B. Roasting of ores
C. Ammonia synthesis
D. Reduction of iron ore
Answer: C
Explanation: Ammonia synthesis is a heterogeneous reaction. Iron is used as a catalyst in the synthesis of ammonia by Haber’s process.

2. Which of the following statements is true about a catalyst?
A. A catalyst remains unchanged in mass at the end of the reaction
B. The chemical composition of catalyst changes at the end of the reaction
C. Catalyst initiates the reaction
D. Catalyst changes the position of reaction equilibrium
Answer: A
Explanation: A catalyst remains unchanged in mass and chemical composition at the end of the reaction. Catalyst cannot initiate the reaction. Catalyst cannot change the position of equilibrium.

3. The free atoms or larger fragments of stable molecules that contain
one or more unpaired electrons are called ____
A. Molecules
B. Complexes
C. Atoms
D. Free radicals
Answer: D
Explanation: The free radicals contain one or more unpaired electrons. They are denoted by a dot on the chemical formula of a substance. A few examples are H., CH_3., etc.

4. The formation of HBr proceeds by ____
A. Free radical, non chain reaction mechanism
B. Free radical, chain reaction mechanism
C. Molecular intermediates, non chain reaction mechanism
D. Transition complexes, non chain reaction mechanism
Answer: B
Explanation: Formation of HBr occurs via free radical mechanism. The Br. radical is first formed. It then combines with H₂ to form HBr and another Br. radical.

5. A bimolecular reaction is the one in which ____
A. One reactant molecule is transformed to product
B. Two product molecules are formed
C. Two reactant molecules produce product(s)
D. No reaction occurs
Answer: C
Explanation: In bimolecular reactions, two reacting species (same or different) react to cause a chemical change. For example,
2HI → H₂ + I₂.

6. An example of termolecular reaction is ____
A. Decomposition of cyclobutane
B. Decomposition of Hydrogen Iodide
C. Decomposition of ammonia
D. Oxidation of Nitric oxide
Answer: D
Explanation: Reaction for oxidation of Nitric oxide is:
2NO + O₂ → 2NO₂
Termolecular reactions are the ones that involve the collision of three reactant molecules.

7. The reaction of the type A → R → S is an example of ____
A. Parallel reaction
B. Series reaction
C. Single reaction
D. Intermediate reaction
Answer: B
Explanation: Series reactions are a form of multiple reactions. For example, oxidation of methanol gives methanal, which in turn gives methanoic acid.

8. The form of reaction, reactant → intermediate, intermediate → product represents the mechanism of ____
A. Non chain reaction
B. Chain reaction
C. Free radical reaction
D. Parallel reaction
Answer: A
Explanation: In non chain reactions, reactants form intermediate in the first step. The intermediates in turn form the products.

9. The reaction in which the rate of reaction is a function on rate constant alone is ____
A. First order reaction
B. Second order reaction
C. Third order reaction
D. Zero order reaction
Answer: D
Explanation: Zero order reaction is the one in which rate does not depend on concentration.
(-r) = k
k → Rate constant

10. Which of the following is an isomerisation reaction?
A. Formation of ammonia from hydrogen and nitrogen
B. Decomposition of hydrogen peroxide to hydrogen and oxygen
C. Conversion of glucose to fructose
D. Combustion reactions
Answer: C
Explanation: Isomerisation is the process in which one molecule gets transformed into another molecule that has absolutely the same atoms which are arranged in a different way. Glucose and fructose, share the same molecular formula: C₆H₁₂O₆. Although all they have the same molecular formula, the arrangement of atoms differs.

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