Page 143 - ICSE Chemistry 8

• Various life processes taking place inside living beings are the result of biochemical reac ons. Amylase,
trypsin, lipase, carbohydrases and pepsin are the most common enzymes present in our body.
• According to the nature of chemical change, chemical reac ons can be classifi ed into the following
types: combina on or synthesis reac ons, decomposi on reac ons, displacement reac ons, double
displacement reac ons and redox reac ons (oxida on-reduc on reac ons).
• Burning of magnesium, reac on of hydrogen and oxygen, reac on of carbon and oxygen, hea ng of
calcium, and reac on of calcium oxide and water are some examples of combina on reac ons.
• Decomposi on reac ons can be of the following types: thermal decomposi on, electric decomposi on
and photodecomposi on.
• Decomposi on of limestone, potassium chlorate, copper hydroxide, ferrous sulphate, mercury (II)
oxide and lead nitrate on hea ng are examples of thermal decomposi on.
• Decomposi on of water, sodium chloride and aluminium oxide on passing of electricity are examples
of electric decomposi on.
• Decomposi on of silver chloride and silver bromine on exposure to light are examples of
photodecomposi on.
• A more reac ve metal displaces a less reac ve metal from its compound during a displacement
reac on. For example, zinc being more reac ve displaces hydrogen from dilute hydrochloric acid and
forms zinc chloride.

• Double displacement reac ons are of two types: precipita on reac on and neutralisa on reac on.
• Reac on of barium chloride and copper sulphate, reac on of sodium chloride and silver nitrate,
reac on of lead nitrate and potassium iodide, and reac on of sodium carbonate and lead nitrate are
some examples of precipita on reac on.
• Reac on of sodium hydroxide and hydrochloric acid, reac on of potassium hydroxide and sulphuric
acid, reac on of zinc oxide and nitric acid, reac on of copper oxide and sulphuric acid, reac on of
lead oxide and nitric acid, and reac on of zinc hydroxide and sulphuric acid are some examples of
neutralisa on reac on.

• Redox reac ons consist of oxida on and reduc on reac ons taking place simultaneously.
• On the basis of vigour of reac on of various metals with oxygen, water and acids, metals have been
arranged in a group of series. In reac vity series, the most reac ve metal is placed at the top whereas
the least reac ve metal is placed at the bo om.
• Oxygen forms oxides by combining with metals and non-metals. We can produce oxides of metals by
hea ng their ores. This can be done in two ways—calcina on and roas ng.
• Oxides are of the following types: acidic oxides, basic oxides, amphoteric oxides and neutral oxides.

EXERCISES

BE PROMPT

A. Fill in the blanks.

1. Substances taking part in a reac on are called _____________ and substances produced in a reac on
are called _____________.
2. When zinc granules are added to dilute sulphuric acid, _________________ is evolved.

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