Page 28 - Chemistry ICSE Class IX

16 ICSE Chemistry – 9
Š When carbon is burnt in air (or oxygen), heat is evolved. Then, the
chemical equation is written as,
C(U) + O (I) o CO (I) + Heat (393 kJ)
2
2
Š The reaction between carbon (C) and sulphur (S) to produce
carbon disulphide (CS ) proceeds with the absorption of heat,
2
K G , it is an endothermic reaction. The chemical equation of this
reaction is written as,
C(U) + 2S(I) o CS (I) – Heat (92 kJ)
2
The reactions with + Heat term on the product side are called
exothermic reactions, while those with – Heat term on the product side
are called endothermic reactions.
ƒ Concentration of the reactants and products. This information is
added to the chemical equation by adding the word dil. (for dilute)
or conc. (for concentrated) before the formulae of the reactants and
products. For example, in the reaction between zinc and dilute
sulphuric acid, the term dil. is added before the formula of sulphuric
acid.
Zn(U) + dil. H SO (CS) o ZnSO (CS) + H (I)
2
4
2
4
ƒ Rate of reaction. This information is not commonly added to the
chemical equation. Sometimes, however, the term fast or slow may
be added over the arrow, if the reaction is HCUV or UNQY. For example,
An explosion is a fast reaction
the reaction between HCl and NaOH in solution is a fast reaction. So,
fast
HCl(CS) + NaOH(CS) o NaCl(CS) + H O(N)
2
What information does a balanced chemical equation
convey
A chemical equation gives two types of information.
1. Qualitative information. A chemical equation provides the following
qualitative information about the reaction. It tells us the,
ƒ names of the reactants which take part in the reaction.
ƒ names of the products formed in the reaction.
2. Quantitative information. A chemical equation gives the following
quantitative information. It tells us about,
ƒ the number of molecules or atoms of reactants and products taking
Burning of gas is an exothermic part in the reaction.
reaction
ƒ the number of moles of each substance involved in the reaction.
ƒ the mass of each substance involved in the reaction.
ƒ mass-mass, mass-volume, volume-volume relationships between the
reactants and products.

ASSIGNMENT 3

Chemical equation

ϭ͘ ĞĮŶĞ ƚŚĞ ƚĞƌŵ ĐŚĞŵŝĐĂů ĞƋƵĂƟŽŶ͘
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