Page 47 - Chemistry ICSE Class IX

Chemical Changes and Reactions 35

N (g) + 3H (g) 2NH (g)
3
2
2
ƒ Oxidation of SO to SO in the presence of V O or NO: Sulphur
3
5
2
2
dioxide (SO ) can be oxidised to sulphur trioxide (SO ) by air in the
3
2
presence of vanadium pentoxide (V O ) catalyst or in the presence of
5
2
nitric oxide (NO) acting as catalyst.
V O catalyst
2SO (g) + O (g) o 2SO (g)
5
2
2
2
3
450°C, 2.5 atm
and
NO(g) catalyst
2SO (g) + O (g) o 2SO (g)
2
3
2
In the reaction using NO as catalyst, the reaction is believed to take
place in two steps. In the rst step, NO takes part in the chemical
reaction and in the second, it is regenerated. As a result, there is no
change in the concentration and structure of NO. That is why it is said
to act as catalyst for this reaction.
ƒ Catalysts are very important for reactions of biological and industrial
importance.
ƒ Catalysts are used in the manufacture of ammonia, sulphuric acid, White polystyrene foam
nitric acid, ethene (C H ), polythene, polystyrene, methanol, vanaspati
4
2
ghee, etc.
ƒ The chemical reactions that take place inside the body of humans,
animals, plants, microorganisms, etc. are catalysed by enzymes.
Enzymes are the catalysts for biochemical reactions. Enzyme-
catalysed reactions are highly speci c.
ASSIGNMENT 1
Physical and chemical changes, Conditions necessary for a chemical reaction to take place
ϭ͘ tŚĂƚ ƚLJƉĞ ŽĨ ĐŚĂŶŐĞ ŽĐĐƵƌƐ ǁŚĞŶ ĂŶ ŝƌŽŶ ƉŝĞĐĞ ŝƐ ŵĂŐŶĞƟƐĞĚ͍ 'ŝǀĞ ƌĞĂƐŽŶƐ͘
Ϯ͘ tŚĂƚ ƚLJƉĞ ŽĨ ĐŚĂŶŐĞ ŝƐ ƚŚĞ ĨĞƌŵĞŶƚĂƟŽŶ ŽĨ ƐƵŐĂƌ͍ 'ŝǀĞ ƌĞĂƐŽŶƐ͘
ϯ͘ tƌŝƚĞ ƚŚĞ ƚŚƌĞĞ ƉƌŽƉĞƌƟĞƐ ŽĨ ŵŝůŬ ǁŚŝĐŚ ĐŚĂŶŐĞ ĚƵƌŝŶŐ ĐƵƌĚ ĨŽƌŵĂƟŽŶ͘
ϰ͘ ůĂƐƐŝĨLJ ƚŚĞ ĨŽůůŽǁŝŶŐ ĐŚĂŶŐĞƐ ŝŶƚŽ ƉŚLJƐŝĐĂů ĂŶĚ ĐŚĞŵŝĐĂů ĐŚĂŶŐĞƐ͗
;ĂͿ ďƌĞĂŬŝŶŐ ŽĨ Ă ŐůĂƐƐ ďĞĂŬĞƌ ;ďͿ ƐĂǁŝŶŐ ŽĨ ǁŽŽĚ ;ĐͿ ĚƌLJŝŶŐ ŽĨ ƉĂŝŶƚ
;ĚͿ ŚĞĂƟŶŐ ŽĨ ĂŶ ŝƌŽŶ ƌŽĚ ;ĞͿ ĚŝŐĞƐƟŽŶ ŽĨ ĨŽŽĚ ;ĨͿ ĞůĞĐƚƌŽůLJƐŝƐ ŽĨ ǁĂƚĞƌ
ϱ͘ EĂŵĞ ƚŚĞ ĐŽŶĚŝƟŽŶƐ ŶĞĐĞƐƐĂƌLJ ĨŽƌ Ă ĐŚĞŵŝĐĂů ƌĞĂĐƟŽŶ ƚŽ ƚĂŬĞ ƉůĂĐĞ͘
ϲ͘ /ůůƵƐƚƌĂƚĞ ƚŚĞ ĞīĞĐƚ ŽĨ ĐĂƚĂůLJƐƚ ŽŶ Ă ƌĞĂĐƟŽŶ ďLJ ŐŝǀŝŶŐ ƚŚĞ ĐŽƌƌĞƐƉŽŶĚŝŶŐ ĐŚĞŵŝĐĂů ĞƋƵĂƟŽŶ͘
ϳ͘ tƌŝƚĞ ƚŚĞ ĐŚĞŵŝĐĂů ĞƋƵĂƟŽŶ ĨŽƌ Ă ƌĞĂĐƟŽŶ ŝŶ ǁŚŝĐŚ ŝƌŽŶ ŝƐ ƵƐĞĚ ĂƐ Ă ĐĂƚĂůLJƐƚ͘
ϴ͘ tŚŝĐŚ ŽĨ ƚŚĞ ĨŽůůŽǁŝŶŐ ďƵƌŶƐ ƌĂƉŝĚůLJ͍
;ĂͿ Ă ůƵŵƉ ŽĨ ĐŽĂů ;ďͿ ĐŽĂů ƉŽǁĚĞƌ
'ŝǀĞ Ă ƌĞĂƐŽŶ ŝŶ ƐƵƉƉŽƌƚ ŽĨ LJŽƵƌ ĂŶƐǁĞƌ͘

Types of Chemical Reactions (or Chemical Changes)

What is meant by a chemical reaction
A chemical process (or change) in which certain substances react together
to form some new substances with different properties is called a chemical
reaction. For example, when hydrogen and oxygen react together, water is
formed.

2H (g) + O (g) o 2H O(l)
2
2
2
hydrogen oxygen water