Problem 68 - A Complete Resource Book in Chemistry for JEE Main

Question

The ability of a catalyst to accelerate the chemical reaction is known as (a) selectivity (b) activity (c) positive catalysis (d) negative catalysis

Step-by-Step Solution

Answer

(b) activity

Step 1: Understanding the Concept of a Catalyst

A catalyst is a substance that increases the rate of a chemical reaction without undergoing any permanent chemical change itself. Its main purpose is to lower the activation energy needed for the reaction to proceed.

Step 2: Differentiating the Given Terms

Here, we need to differentiate between the terms provided: selectivity, activity, positive catalysis, and negative catalysis. - **Selectivity** refers to the ability of a catalyst to direct a reaction to produce a specific product. - **Activity** refers to the ability of a catalyst to speed up the reaction rate. - **Positive catalysis** is the general process of speeding up a chemical reaction. - **Negative catalysis** involves slowing down a reaction.

Step 3: Matching the Concept to the Option

The question asks for the ability of a catalyst to accelerate a chemical reaction. From our understanding: - **Selectivity** does not refer directly to speed but to product preference. - **Activity** specifically describes the ability to increase the reaction rate. - **Positive catalysis** is too broad as it simply means any increase in reaction rate but isn't a property of the catalyst. - **Negative catalysis** is about slowing, not speeding up reactions.

Step 4: Determining the Correct Answer

Given the definitions, the best term representing the catalyst's ability to speed up a reaction is **activity**. This term describes exactly what the question asks for.

Key Concepts

Selectivity in Catalysis

Selectivity in catalysis is all about directing a chemical reaction to yield a specific and desired product. Imagine a catalyst as a helpful guide in a chaotic world of chemical reactions. It chooses the path that ensures the end result is the one you need. Selectivity doesn’t just mean getting any product faster; it means getting the **right** product. This is crucial in industrial processes where different products can arise from the same reactants, but only one is commercially desirable. Catalysts achieve selectivity through:

• **Specific interaction**: Forming intermediate species with reactants, steering the reaction.
• **Structural properties**: The shape and size of catalyst particles affecting which molecules can approach and react.
• **Environmental conditions**: Temperature and pressure conditions that optimize the right reaction pathway.

By understanding and controlling these factors, chemists can manipulate catalysts to not just speed up reactions, but guide them to produce only the most useful products needed.

Positive and Negative Catalysis

Positive and negative catalysis are two sides of how catalysts can alter a chemical reaction's pace. ### Positive Catalysis This is the more commonly known form. In positive catalysis, the catalyst works its magic by lowering the activation energy, thereby increasing the rate of the reaction. Think of it as a greasing up a machine so it operates faster and more efficiently. Enzymes in biological systems are classic examples of positive catalysts. They allow complex reactions in the body to occur rapidly at relatively low temperatures. ### Negative Catalysis On the flip side, we have negative catalysis. Here, the catalyst's role is to deliberately slow down the reaction. While this might seem counterproductive at first, it is invaluable in situations where reactions might otherwise proceed too quickly, leading to undesirable or dangerous results. For example, inhibitors are used in chemical processes to prevent spontaneous decomposition or combustion. In both cases, the catalysts remain unchanged by the reaction, whether speeding it up or slowing it down, highlighting the versatile and crucial roles they play in chemistry.

Activation Energy in Reactions

Activation energy is the minimum amount of energy required for a chemical reaction to take place. It’s like the initial push needed to get a car rolling down a hill. ### Importance of Activation Energy Without sufficient activation energy, reactants don't have the oomph to transform into products. The higher the activation energy, the slower the reaction at a given temperature. Conversely, lowering this energy requirement tends to speed up the reaction rate. ### Role of Catalysts This is where catalysts step in. By providing an alternative reaction pathway with lower activation energy, catalysts make it easier for reactions to occur. This doesn’t mean they do the reactants’ work, but rather they make the work easier to accomplish. ### Real-World Impact In practical scenarios, think about using a flame to start cooking. The flame supplies activation energy. Similarly, in chemical plants, catalysts act as that 'spark' making reactions efficient and economically feasible. Understanding activation energy helps chemists innovate in creating new catalysts to make reactions faster, safer, and more controlled, furthering advancements in industries and research.