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Catalysts and Enzymes

Grade 8 Science Worksheets

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Speeding up Chemical Reactions

Ever noticed that sugar dissolves faster in hot water than in cold? Or that food cooks quicker on high flame? Temperature is an important factor in these matters. It is equally important in many chemical reactions. It has been experimentally observed that every 50oFrise in temperature doubles,and sometimes triples, the speed of chemical reactions.

Temperature is a measure of the average kinetic energy of molecules. At higher temperatures, molecules in motion tend to remain in motion, thereby increasing their ability to collide with molecules of other reactants to activate a chemical reaction. This is the Collision Theory, according to which molecules only react if they have sufficient energy for a reaction to take place.

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There are other ways to speed up chemical reactions –

  • Increasing the concentration of reactants – more molecules are available for collision
  • Increasing the surface area of reactants – larger surface area means greater collisions

Very often, chemists use an additional substance to alter the rate of chemical reactions. This additional substance is called a Catalyst and the chemical process using a catalyst is known as Catalysis.


Catalysts are used in industry to speed up many chemical reactions which otherwise would take place too slowly.


These are some of their inherent characteristics –

  1. A catalyst is purposeful in nature – a specific catalyst works only for a specific reaction.
  2. A catalyst provides a chemical pathway for a reaction to proceed far more rapidly in its presence than in its absence.
  3. Often, a catalyst reacts with one of the reactants to produce an intermediate chemical product which then reacts more readily with the other reactant to form the desired end product.
  4. A catalyst is not consumed by the chemical reaction, nor is it a part of the resulting products of the reaction in anyway.

Catalysts have a wide variety of uses in our daily lives and in industry –

  • Cobalt-based catalysts to make smooth paper from wood pulp
  • Zinc chloride as a catalyst to make synthetic fibers like nylon and rayon
  • Catalysts in the manufacture of a wide variety of plastics from milk jugs to CDs to helmets
  • Ammonia synthesis – nitrogen reacts with hydrogen at high temperature and pressure in the presence of iron as a catalyst to produce liquid ammonia
  • Manufacture of Sulfuric acid – Sulfur dioxide and oxygen, passed over hot vanadium oxide as a catalyst, unite to form sulfur trioxide, which in turn combines with water to make sulfuric acid.
  • Adding potassium permanganate as a catalyst to hydrogen peroxide hastens its decomposition into water and oxygen gas.
  • Cars use catalytic converters containing platinum, which converts harmful carbon monoxide gas into less harmful carbon dioxide gas.

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Many acids and bases also act as catalysts, both individually and together. They lend themselves to catalysis on account of their proton-donor and proton-acceptor characteristics. See also: Acid, bases and pH Indicators.

Some examples of acids and bases as catalysts –

  • Sulfuric acid is a catalyst used for the decomposition of sucrose into glucose and fructose
  • Sulfuric acid is also used as a catalyst in the polymerization of unsaturated hydrocarbons.
  • Amorphous silica-alumina, an acid catalyst, is used in the conversion of petroleum hydrocarbons to gasoline.
  • Sodium- and potassium-hydroxides are used as catalysts in industrial bio-diesel production
  • Base-catalyzed aldol condensation
  • Base-catalyzed manufacture of polyurethane foam


Enzymes are naturally occurring proteins that act as catalysts in many biochemical reactions. They are organic catalysts that perform important and critical functions in living beings. The human body has thousands of enzymes enabling respiration, sight, muscle movement, nerve function, digestion and much more.

Enzymes at work!

Some enzyme examples –

  • Probiotic cultures which ferment milk to make yogurt
  • Single-celled micro-organisms called Yeasts produce enzymes which are used in baking breads and pizza dough, in wine-making and many other fermentation processes
  • Rennet is used for separating milk into curd and whey and in the production of cheese
  • Photosynthesis in plants
  • Lipase enzymes help digest fat
  • Liver enzymes break down body toxins
  • Trypsin breaks proteins into amino acids

Check Point

  1. Which is not a method to speed up a chemical reaction?
    1. Heat
    2. Inert gases
    3. Use of catalysts
    4. Concentration of reactants
    5. Surface area of reactants
  2. The chemical process of adding a substance to speed up a chemical process is called ______.
  3. Catalysts are often completely consumed in a chemical reaction. (True/False)
  4. Many acids and bases act as catalysts. (True/False)
  5. Naturally occurring proteins that act as catalysts in many biochemical reactions are called ______.

Answer Key

  1. b) Inert gases
  2. Catalysis
  3. False
  4. True
  5. Enzymes

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