This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Surface Chemistry – Catalysis”.
1. How does a catalyst change during a reaction?
Explanation: Yes, a catalyst can be changed physically in a chemical reaction but by definition a catalyst is not consumed as a reactant. It must be regenerated back into its original form after the reaction has taken place. Its function is to lower the reaction potential allowing the reaction between reactants to take place.
2. Which of the following does not occur at the interface of phase?
b) Heterogeneous catalysis
c) Homogeneous catalysis
Explanation: A catalyst is a substance which increases the rate of reaction but itself does not undergo any chemical change during the reaction. In homogeneous catalysis, the reactants and catalyst are in the same phase (i.e. liquid or gas).
3. Promoter decreases the activity of catalyst.
Explanation: A catalytic promoter is a substance which increases the activity of the catalyst but itself does not act as a catalyst. Eg: In the manufacture of ammonia by Haber’s process, Molybdenum acts as a catalytic promoter for the iron catalyst.
4. Which of the following decreases the rate of reactions?
a) Catalytic promoters
b) Homogeneous catalyst
c) Catalytic poison
d) Heterogeneous catalyst
Explanation: A catalytic poison is a substance which destroys the activity of the catalyst even if it is present in trace amounts. Eg: In the manufacture of sulphuric acid by contact process, any arsenic impurity present in the reacting gases will destroy the activity of vanadium pentoxide catalyst.
5. Which of the following is used as a catalyst for the following reaction?
CH3COOC2H5 + H2O ——–> CH3COOH + C2H5OH
b) Hydrochloric acid
c) Sulphuric acid
d) Nitrous acid
Explanation: In acid hydrolysis, water splits the ester bond. The hydrogen atom joins to the oxygen atom in the OR part of the original ester and the OH of the water joins to the carbonyl carbon atom. So hydrochloric acid is preferred.
6. What is the amount of intermediate formed when initial amount is 300 and final amount is 700?
Explanation: The amount of the intermediate formed is nothing but the difference in the compounds used.
Initial amount = 300
Final amount = 700
Hence, the amount of intermediate formed is 700 – 300 = 400.
7. Which of the following statements is not correct?
a) The efficiency of a solid catalyst depends upon its surface area
b) Catalyst operates by providing alternate path for the reaction that involves a lower energy of activation
c) Catalyst lowers the energy of activation of the forward reaction without affecting the energy or activation of the backward reaction
d) Catalyst does not affect the overall enthalpy change of the reaction
Explanation: A catalyst provides an alternate pathway for the reaction that has lower activation energy. When activation energy is lower, more reactant particles have enough energy to react and so the reaction occurs faster.
8. Which of the following statements is not correct?
a) Catalyst is not involved in the reaction
b) The concentration of a catalyst remains constant throughout the progress of chemical reaction
c) The mechanism of catalytic reactions may vary from reaction to reaction
d) NO acts as a homogenous catalyst in the oxidation of SO2 to SO3
Explanation: Catalyst is a substance which increases or decreases the rate of reaction but itself does not undergo any chemical change during the reaction. Catalysts that increase the rate are called positive catalysts and the catalysts that decrease the rate are called negative catalysts.
9. Which of the following does it increase the rate of catalyst?
a) Decreasing Ea
b) Increasing Ea
c) Increasing pressure
d) Increasing entropy
Explanation: A catalyst lowers the activation energy and so more particles can attain activation energy, thus a faster rate of reaction. Only a small amount of catalyst is required. Increasing the amount of catalyst used will not increase the rates of reaction beyond a certain point.
10. Which of the following is present at the time of cracking of hydrocarbons?
Explanation: The zeolites used in catalytic cracking are chosen to give high percentages of hydrocarbons with between 5 and 10 carbon atoms – particularly useful for petrol. The zeolite catalyst has sites which can remove a hydrogen from an alkane together with the two electrons which bound it to the carbon.
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