Iron metal reacts with elemental oxygen to form rust according to the unbalanced reaction, Fe(s) + O2(g) → Fe2O3(s),. What is the coefficient of the oxygen, O2(g), in the balanced reaction? a
1
b
2
c
3
d
4

c. 3

Explanation:

The unbalanced reaction expression is given as:

          Fe  +  O₂  →   Fe₂O₃  

To balance the expression gives the coefficient of oxygen.

Assign the coefficients a,b, c and use a mathematical approach to solve this problem:

             aFe  +  bO₂  →  cFe₂O₃

Conserving Fe: a  = 2c

                    O:  2b  = 3c

Now let c = 1, a  = 2, b  =

  Multiply through by 2,

             a = 4, b = 3 and c  = 2

               4Fe  +  3O₂  →   2Fe₂O₃  

The coefficient of O₂ is 3

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