Balancing by Inspection

Balancing equations is basically a process of trial and error, called inspection, but a few hints can help.

1. Balance atoms that appear only once in reactant and product first, and atoms that appear more than once last.

Example #1:

	Reactant		Product
	___C3H8 (g)+ ___O2 (g)		___CO2 (g) + ___H2O (g)
Step 1	Balance atoms that appear only once first (C and H ) _1_C3H8 (g)+ ___O2 (g)		_3_CO2 (g) + _4_H2O (g)
Step 2	Balance atoms that appear more than once last (O) _1_C3H8 (g)+ _5_O2 (g)		_3_CO2 (g) + _4_H2O (g)

2. Balance polyatomic ions as a group , for example SO₄ ^2- ion. Caution: The ion must remain the same in reactant and product.

Example #2:

	Reactant		Product
	___Ca(NO3)2 (aq) + ___Na3PO4 (aq)		___Ca3(PO4)2 (s) + ___NaNO3 (aq)
Step 1	Balance atoms that appear only once ( Ca , Na ) _3__Ca(NO3)2 (aq) + ___Na3PO4 (aq)		___Ca3(PO4)2 (s) + _3__NaNO3 (aq)
Step 2	Balance atoms in ions as groups (PO4 ; NO3 ) _3__Ca(NO3)2 (aq) + _2__Na3PO4 (aq)		_1__Ca3(PO4)2 (s) + _6__NaNO3 (aq)

3. In some cases the # of atoms of an element in the reactants may be odd, while the # in the products will always be even (due to a even subscript). In this case you need to double the balance of all atoms already balanced and continue the balancing.

Example #3:

	Reactant		Product
	___CuFeS2 (s) + ___O2 (g)		___Cu (s) + ___FeO (s) + ___SO2 (g)
Step 1	Balance atoms that appear only once first _1_CuFeS2 (s) + ___O2 (g)		_1_Cu (s) + _1_FeO (s) + _2_SO2 (g)
Step 2	Balance oxygen now. Notice that there is five atoms in the products but the reactants will always be even. To balance, double all balances already made. Now continue by balancing the oxygen
	_2_CuFeS2 (s) + _5_O2 (g)		_2_Cu (s) + _2_FeO (s) + _4_SO2 (g)

Balancing Activities The following game called Chem balancer, allows you to practice balancing equations by inspection. The following Balancing Equations worksheet contains 40 practice questions and answers to help you practice your balancing

Assignment #2: Balancing using inspection Balance the following chemical equations by inspection ; 1. ___K2O + ___H2O -------> ____KOH 2. ___KOH +___ H3PO4 -------> ___K3PO4 + ___H2O 3.___CaCl2 + ___HNO3 -------> ___Ca(NO3)2 + ___HCl 4.___FeCl3 + ___KOH -------> ___KCl + ___Fe(OH)3 5 ___.NaClO + ___H2S -------> ___NaCl + ___H2SO4 6. ___Ag2S + ___HNO3 -------> ___AgNO3 + ___NO + ___S + ___H2O 7. ___I2 + ____Na2S2O3 -------> ___ Na2S4O6 + ___NaI 8. ___Fe + ___CuNO3 -------> ___Fe(NO3)2 + ___Cu 9. ___MgCl2 + ___NH4NO3 -------> ___Mg(NO3)2 + ___NH4Cl 10. ___Al + ___H2SO4 -------> ___Al2(SO4)3 + ___H2 Click to download pdf file