MCQ Detailed View

In chemical kinetics, a catalyst is a substance that increases the speed of a reaction without being consumed in the process. Normally, catalysts lower the activation energy and make reactions proceed faster. However, in some cases, the opposite effect occurs. When a substance decreases the rate of a chemical reaction, the phenomenon is called negative catalysis.

Negative catalysis is also known as inhibition. An inhibitor is a substance that slows down or completely prevents a reaction by interfering with the reacting molecules or by stabilizing the transition state in an unfavorable way. Unlike positive catalysts, inhibitors increase the effective activation energy, making the reaction slower.

Examples of inhibition include:

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  Auto-oxidation reactions of organic compounds such as aldehydes, which are slowed down by the addition of antioxidants like hydroquinone.

  
  


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  Corrosion prevention, where inhibitors are added to reduce the rate of metal oxidation.

  
  


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  In biological systems, many enzyme inhibitors act as negative catalysts, reducing the rate of biochemical reactions.

  
  

It is important to distinguish inhibition from other catalytic processes. Auto catalysis occurs when one of the reaction products itself acts as a catalyst, speeding up the reaction. Self catalysis refers to the same idea where the reaction is accelerated by its own products. Enzyme catalysis involves biological catalysts (enzymes) that generally increase reaction rates. None of these represent negative catalysis.

Therefore, the correct answer is inhibition, which is the accepted term for negative catalysis.

This concept is important in physical chemistry, especially in kinetics, industrial chemistry (to prevent unwanted side reactions), and biological systems where inhibitors regulate enzyme activity.