1. Catalysts work by _________.
A. Increasing the concentration of reactants
B. Decreasing the rate of reaction
C. Providing an alternative reaction pathway with a lower activation energy
D. Increasing the reaction order
ANSWER: C.Providing an alternative reaction pathway with a lower activation energy
SOLUTION :During a chemical reaction, the bonds between the atoms in molecules are broken, rearranged, and rebuilt, recombining the atoms into new molecules. Catalysts make this process more efficient by lowering the activation energy, which is the energy barrier that must be surmounted for a chemical reaction to occur.
2. A catalyst can ___________
A. Increase the rate of reversible reaction in both the forward and reverse directions
B. Increase the rate of a reversible reaction only in the forward direction
C. Decrease the rate of a reaction
D. Increase the activation energy of a reaction
ANSWER: A.Increase the rate of reversible reaction in both the forward and reverse directions
SOLUTION: A catalyst can speed up a chemical reaction, or lower the temperature or pressure needed to start one, without being consumed during the reaction. Catalysts can also change the products of a chemical reaction, such as the heat of reaction, the time it takes the reaction to proceed, and the potential energy of the reactants.
3. Which of the following statements about heterogeneous catalysts is true ?
A. They are always in the same phase as the reachants
B. They can be easily seperated from the reaction mixture
C. They are the chemical composition of the reactants
D. They are highly soluble in the reaction solvent
ANSWER : B.They can be easily seperated from the reaction mixture
SOLUTION: They can be easily seperated from the reaction mixture
4. Poisoning of a catalyst refers to _________.
A. Making the catalyst more active
B. Reducing the catalyst’s activity by introducing unwanted substances
C. Increasing the catalyst’s selectivity
D. Promoting the catalyst’s stability
ANSWER: B.Reducing the catalyst’s activity by introducing unwanted substances
SOLUTION: Catalyst poisoning is the partial or total deactivation of a catalyst by a chemical compound.
5. Selectivity of a catalyst refers to ________
A. Its ability to remain unchanged during a reaction
B. Its ability to promote multiple side reactions
C. Its ability to favor the formation of a specific product in a reaction
D. Its ability to speed up any chemical reaction
ANSWER: C.Its ability to favor the formation of a specific product in a reaction
SOLUTION: Catalysts are highly specific compounds. They have an ability to direct the reaction to yield a particular product. The reaction with same reactants but different catalyst may yield different products. This is termed as the selectivity of catalyst.
6. Promoters in catalysis are substances that _______.
A. Decrease the catalytic activity
B. Enhance the selectivity of the catalyst
C. Increase the reaction rate without being consumed
D. Poison the catalyst
ANSWER: C.Increase the reaction rate without being consumed
SOLUTION: Substances which themselves are not catalysts but when mixed in small quantities with the catalysts increase their efficiency are called as Promoters. Promoters are substances which increase the efficiency of catalyst.
7. Which of the following factors can influence the effectiveness of a catalyst?
A. Temperature and pressure only
B. Concentration of reactants only
C. Temperature, concentration of reactants , and catalyst particle size
D. Catalyst particle size only
ANSWER: C.Temperature, concentration of reactants , and catalyst particle size
SOLUTION :
The factors that influence the catalytic reactivity of a catalyst include the environment of the active sites and the interactions between the catalyst and the reactant molecules. Metal Catalysts for Heterogeneous Catalysis: From Single Atoms to Nanoclusters and Nanoparticles.
8. Autocatalysis is a phenomenon where ______.
A. The catalyst accelerates its own decomposition
B. The reaction rate increases as the reaction progresses
C. The catalyst is consumed in the reaction
D. The reaction rate remains constant
ANSWER: B.The reaction rate increases as the reaction progresses
SOLUTION: The reaction rate increases as the reaction progresses
9. A homogeneous catalyst is _________.
A. Always in the same phase as the reactants
B. Typically a solid in solution
C. Insoluble in the reaction medium
D. Used exclusively in gas – phase reactions
ANSWER: A.Always in the same phase as the reactants
SOLUTION: A homogeneous catalyst is present in the same phase as the reactants. Gas-phase reactions and reactions in solution are homogeneous reactions and we have already discussed several examples where catalyst and reactants are all in the same phase.
10. In the manufacture of ammonia (NH3) through the Haber – Bosch process, which catalyst is commonly used ?
A. Platinum
B. Palladium
C. Iron
D. Nickel
ANSWER: C.Iron
SOLUTION:
Finely divided iron is used as catalyst in the manufacture of ammonia by Haber’s process.