Panel 2: Exploring the meaning of chemical reactions

Unbalanced reaction:

H2 + O2 H2O

Balanced reaction, undetermined coefficients:

aH2 + bO2 cH20
reactants products
hydrogen atoms: 2a 2c
oxygen atoms: 2b c

Therefore 2a = 2c (that is, a=c), and 2b=c.

Correct, balanced equation:

2H2 + O2 2H2O

Balanced equation, but coefficients not whole numbers:

H2 + 1/2O2 H20

This reaction is balanced, but its coefficients are not least whole numbers:

4H2 + 2O2 4H20