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CBSE Class 10 Answered

HOw to write the chemical equation and to balance it ?
Asked by Rajat Jain | 08 Aug, 2012, 11:09: AM
Expert Answer
Writting a chemical equation:
A chemical equation is a chemist’s shorthand expression  for describing a chemical change. 
Points to be remembered ;
  1. reactants are written on the left hand side of the arrow and products on the right hand side
  2. The conditions of the reaction like temperature and pressure can be wriiten above the arrow or below the arrow.(this includes pressure temperature or any catalyst if used,etc.)
  3. the state of the reactants and products are written in bracket along with the elements.
  4. Two substances reacting together are shown by introducing a 'plus' sign between them
  5. escaping gases are shown by upward arrow whereas a downward arrow shows the solid formed.
  6. equilibrium arrow shows the completion of the reaction if the forward arrow is large it shows euilibrium is towards forward direction and vice versa.
Balancing a chemical equation is shown below with the help of an example:
 In order to have quantitative information about the reaction, the equation must be balanced so that it conforms to the Law of Conservation of Matter.  That is, there must be the same number of atoms of each element on the right hand side of the equation as there are on the left hand side.
 If the number of atoms of each element in the equation above are counted, it is observed that there are 1 atom of Fe and 2 atoms of O on the left side and 2 atoms Fe and 3 atoms of O on the right. 
       Fe  +  O2  ?    Fe2O3 
Left side:               Right side: 
 1 atom Fe                2 atoms Fe   
2 atoms O                3 atoms O
  •  The balancing of the equation is accomplished by introducing the proper number or coefficient before each formula.  To balance the number of O atoms, write a 3 in from of the O2 and a 2 in front of the Fe2O3:
 Fe  + 3 O2  ?   2 Fe2O3
  • The equation, above, now has 6 atoms of O on each side, but the Fe atoms are not balanced.  Since there is 1 atom of Fe on the left and 4 atoms of Fe on the right, the Fe atoms can be balanced by writing a 4 in front of the Fe: 
4 Fe  +  3 O2  ?   2 Fe2O3
  • This equation is now balanced.  It contains 4 atoms of Fe and 6 atoms of O on each side of the equation.  The equation is interpreted to mean that 4 atoms of Fe will reaction with 3 molecules of O2 to form 2 molecules of Fe2O3

It is important to note that the balancing of an equation is accomplished by placing numbers in front of the proper atoms or molecules and not as subscripts.  In an equation, all chemical species appear as correct formula units.  The addition (or change) of a subscript changes the meaning of the formula unit and of the equation.  Coefficients in front of a formula unit multiply that entire formula unit.

Answered by | 08 Aug, 2012, 01:05: PM
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