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ICSE Class 8 Answered

define catalyst. describe the use of a catalyst in a chemical reaction with a suitable example ?
Asked by nathsantanukumar | 09 May, 2018, 07:01: PM
answered-by-expert Expert Answer

Catalyst and their actions

A catalyst is a substance which either increases or decreases the rate of a chemical reaction without itself undergoing any chemical change during the reaction.

Some chemical reactions need a catalyst to change the rate of the reaction.

1) Positive catalyst: It increases the rate of reaction.

Examples:

 On heating to 700°C, potassium chlorate decomposes to evolve oxygen gas.

But when manganese dioxide is mixed with it, the decomposition takes place at a much lower temperature, at about 300°C. In this reaction, manganese dioxide acts as a catalyst and remains unaffected.

 

2)  Negative catalyst: It decreases the rate of reaction.

Example:

Phosphoric acid acts as a negative catalyst to decrease the rate of decomposition of hydrogen peroxide.

 Alcohols also act as a negative catalyst in certain chemical reactions.

   

Answered by Varsha | 10 May, 2018, 09:57: AM
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