40 Questions
What is the primary function of a catalyst in a chemical reaction?
To increase the reaction rate without changing the equilibrium state
What happens to the physical properties of a catalyst after a reaction?
They may be changed, but not consumed
What is meant by the 'selectivity' of a catalyst?
The ability to induce the formation of particular products
What is the effect of a catalyst on the equilibrium state of a reaction?
It does not affect the equilibrium state
What is an example of a positive catalytic process?
The catalytic decomposition of H2O2
What is an example of a negative catalytic process?
The esterification of alcohol in the presence of glycerol
What is the role of a catalyst in terms of energy?
To neither provide nor absorb energy
What is true about the chemical composition of a catalyst after a reaction?
It remains unchanged
What is the significance of a small quantity of catalyst in a reaction?
It is sufficient to catalyze almost unlimited reactions
What is the role of a catalyst in a reaction?
To alter the speed of the reaction
What is the purpose of a promoter in a catalytic reaction?
To increase the efficiency of the catalyst
What is the effect of increasing the temperature on a catalyst?
It increases the catalytic power of the catalyst up to a certain point
What is the characteristic of a catalyst that enables it to accelerate numerous reactions with a limited quantity?
Stability
What is the significance of anhydrous aluminium chloride in the Friedel-Craft reaction?
It is required in a relatively large amount
What is the difference between a catalyst and a promoter?
A catalyst has a catalytic effect, while a promoter has little or no catalytic effect
What is the primary role of a catalyst in a reaction?
Increasing or decreasing the overall rate of reaction
What is the result of a catalyst being present in a reaction?
The reaction will proceed at a faster rate than without the catalyst
What is the term for substances added in small quantities to enhance a catalyst's efficiency?
Promoters
How does the surface area of a catalyst influence the reaction rate?
Increasing surface area increases the reaction rate
What is the purpose of copper ion in the oxidation of Na2SO3?
To act as a catalyst
Which of the following is not a key requirement for industrial catalysts?
Reactivity
What is the correct priority order for target quantities in industrial catalysts?
Stability > Selectivity > Activity
What is a catalytic promoter?
A substance that increases the efficiency of a catalyst
How does temperature influence the catalytic power of a catalyst?
Increasing temperature initially increases, then decreases catalytic power
What is the temperature at which a catalyst's catalytic activity is maximum?
Optimum temperature
Why is the reaction faster when MnO 2 is present as a powder than as granules?
Because the powder has a larger surface area
What is the order of priority for target quantities in industrial catalysts?
Selectivity > Stability > Activity
What is the main method for describing the role of catalysts in chemical reactions?
The catalytic cycle
What is the primary requirement for an industrial catalyst?
It must have a realistic rate of reaction
What is the purpose of the catalytic cycle?
To describe the role of catalysts in chemical reactions
What is the effect of increasing the surface area of a catalyst?
The reaction rate increases
What is the term for the reduction of activation energy due to the addition of a foreign substance?
Catalytic process
What enables a catalyst to remain unchanged at the end of a reaction?
Stability
What is the ability of a catalyst to induce the formation of particular products?
Selectivity
In the Haber's process, what substance enhances the activity of finely divided iron?
Molybdenum
What is a characteristic of a catalytic cycle?
It is a multistep reaction mechanism involving a catalyst
How does the surface area of a catalyst influence the reaction rate?
Larger surface area increases the reaction rate
What is the role of a catalytic promoter in a reaction?
To increase the efficiency of the catalyst
How does temperature influence the catalytic power of a catalyst?
Increasing temperature initially increases, then decreases catalytic power
What is true about the addition of a catalyst in small amounts?
The catalyst reduces the activation energy
Study Notes
Introduction to Catalysis
- Catalysis is the key to chemical transformations, where a catalyst is a substance that alters the chemical rate without changing its own chemical composition when added in small amounts.
Types of Catalysts
- A catalyst can accelerate both forward and backward reactions in the same proportion, e.g., HCl accelerates hydrolysis of ester and esterification of alcohol.
- A catalyst can also accelerate only the forward chemical reaction, e.g., catalytic decomposition of H2O2 in presence of metals.
- In some cases, a catalyst can accelerate the backward reaction, e.g., presence of glycerol as a catalyst.
General Characteristics of Catalysis
- A catalyst does not change, consume, deactivate, or destroy at the end of the reaction, but its physical properties may change.
- A small quantity of catalyst is generally sufficient to catalyze almost unlimited reactions, making it economically important.
- The rate of reaction is directly proportional to the concentration of the catalyst in many homogeneous catalytic reactions.
- A catalyst cannot initiate the reaction, but only increases or decreases the overall rate of reaction.
Catalytic Promoters
- Substances that increase the efficiency of catalysts when mixed in small quantities are called promoters or activators.
- Examples include molybdenum in Haber's process for the synthesis of ammonia and chromic oxide in the manufacture of methyl alcohol from water gas.
Influence of Temperature
- Increasing temperature initially increases the catalytic power of a catalyst, but after a certain temperature, its power begins to decrease.
- Each catalyst has an optimum temperature at which its catalytic activity is maximum.
Effect of Surface Area
- The more finely divided (powdered) the catalyst is, the faster the reaction happens.
- For example, the decomposition of hydrogen peroxide in presence of MnO2 as catalyst is much faster when the catalyst is present as a powder than as granules.
Requirements of Industrial Catalysts
- A catalyst must have a realistic rate of reaction (activity), achieve an acceptable selectivity for the desired products, and be sufficiently stable under operating conditions.
- The priority order for target quantities is selectivity > stability > activity.
Catalytic Cycle
- The catalytic cycle is a multistep reaction mechanism that involves a catalyst and is usually written as a sequence of chemical reactions in the form of a loop.
- Catalysts are regenerated, and catalytic cycles describe the role of catalysts in chemical reactions.
Learn about the concept of catalysis, its role in chemical transformations, and the types of catalysts. Discover how catalysts alter chemical reaction rates without changing the composition of the reactants.
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