Page 127 - ICSE Chemistry 8

Catalyst and Enzyme

Catalyst

A catalyst is a substance that alters the rate of a chemical reac on without itself undergoing any
permanent chemical change during the reac on.
Examples:

• When a pinch of manganese (IV) oxide is added
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to hydrogen peroxide in a test tube, there is an
immediate eff ervescence. A glowing splinter placed Catalysts reduce the amount of
near the mouth of the test tube will relight showing energy needed to ac vate chemical
that oxygen is being evolved. Here manganese (IV) reac ons.
oxide acts as a catalyst.
• When potassium chlorate is heated strongly, oxygen is liberated. However, if some manganese
oxide is mixed with potassium chlorate, oxygen is liberated at a faster rate and without hea ng.
Here, manganese oxide acts as a catalyst.
MnO
2KClO (s) 300°C 2 2KCl(s) + 3O (g)
2
3
Potassium chlorate Potassium chloride Oxygen
• Photosynthesis in green plants takes place in the presence of chlorophyll that acts as a catalyst.

There are two types of catalysts: posi ve catalyst and nega ve catalyst.
• Posi ve catalyst: A catalyst that increases the rate of a chemical reac on is called a posi ve catalyst.
• Nega ve catalyst: A catalyst that decreases the rate of a chemical reac on is called a nega ve
catalyst.
Biocatalyst or Enzyme

When a substance acts as a catalyst in a biochemical
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reac on, then it is called a biocatalyst or an enzyme.
Various life processes taking place inside living beings Richard Mar n Willstä er (1872–1942) was
are the result of biochemical reac ons. Amylase, a German organic chemist. He won a Nobel
Prize in 1915 for his research on plant pigment,
trypsin, lipase, carbohydrases and pepsin are the
especially chlorophyll.
most common enzymes present in our body. They are
involved in the diges on of starch, fats and proteins.

• Pepsin is present in the stomach and helps in the breakdown of proteins into amino acids. The
enzymes involved at diff erent stages of protein diges on are collec vely known as proteases.
• Trypsin and lipase are present in the small intes ne and help to breakdown starch, fats and proteins
into glucose, fa y acids and amino acids, respec vely.

• Enzyme carbohydrase is specifi c to the diges on of carbohydrates.
• Enzyme maltase, present in the living cells of yeast, helps in the conversion of maltose
(a carbohydrate) into glucose.

• Enzyme zymase, present in the living cells of yeast, helps in the fermenta on of glucose in alcohol.

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