Humboldt State University ® Department of Chemistry

Richard A. Paselk

	Introductory Chemistry	Fall 2005
Exercise: Balancing by Inspection	© R. Paselk 2005
	Worked Examples
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Equation Balancing by Inspection

Balance the equations below by providing the proper coefficients:

1. Al_(s) + Fe₂O_{3 (s)} Fe_(s) + Al ₂O_{3 (s)}

We can make a table to keep track of the numbers of atoms on both sides:

Looking at the table, oxygen is already balanced, and we simply need to multiply Al and Fe by 2 by adding the appropriate coeficients:

2 Al_(s) + Fe₂O_{3 (s)} 2 Fe_(s) + Al ₂O_{3 (s)}

The table of atoms now shows all are balanced:

2. KClO_{3 (s)} + heat KCl_(s) + O_{2 (g)}

Making a table to keep track of the numbers of atoms on both sides:

Looking at the table, oxygen is the only atom not balanced, but this time we must multiply KClO₃by 2 and by O₂ 3:

2 KClO_{3 (s)} + heat KCl_(s) + 3 O_{2 (g)}

Updating the table we get:

	Reactants	Products
K	2	1
Cl	2	1
O	6	6

Addding a coefficient of 2 for KCl will then baslance the equation:

2 KClO_{3 (s)} + heat 2 KCl_(s) + 3 O_{2 (g)}

 

3. C₄H_{10 (g)} + O_{2 (g)} CO_{2 (g)} + H₂O_(g)

C₄H_{10 (g)} + 13/2 O_{2 (g)} 4 CO_{2 (g)} + 5 H₂O_(g)

With integral coefficients:

2 C₄H_{10 (g)} + 13 O_{2 (g)} 8 CO_{2 (g)} + 10 H₂O_(g)

4. N_{2 (g)} + H_{2 (g)} NH_{3 (g)}

N_{2 (g)} + 3 H_{2 (g)} 2 NH_{3 (g)}

5. P_{4 (s)}+ F_{2 (g)} PF_{5 (g)}

P_{4 (s)}+ 10 F_{2 (g)} 4 PF_{5 (g)}

6. Cu_(s) + AgNO_{3 (aq)} Cu(NO₃)_{2 (aq)} + Ag_(s)

Cu_(s) + 2 AgNO_{3 (aq)} Cu(NO₃)_{2 (aq)} + 2 Ag_(s)

7. Fe_(s) + O_{2 (g)} Fe₂O_{3 (s)}

4 Fe_(s) + 3 O_{2 (g)} 2 Fe₂O_{3 (s)}

8. FeCl_{3 (s)} + H₂O_(l) HCl_(aq)+ Fe(OH)_{3 (s)}

FeCl_{3 (s)} + 3 H₂O_(l) 3 HCl_(aq)+ Fe(OH)_{3 (s)}

9. Zn(NO₃)_{2 (s)} + heat ZnO_(s) + NO_{2 (g)} + O_{2 (g)}

2 Zn(NO₃)_{2 (s)} + heat 2 ZnO_(s) + 4 NO_{2 (g)} + O_{2 (g)}

10. H₃PO_{4 (l)} + heat H₂O_(l) + P₄O_{10 (s)}

4 H₃PO_{4 (l)} + heat 6 H₂O_(l) + P₄O_{10 (s)}