How do I balance an equation with one side

I understand balancing an equation fairly well, but how does one balance an equation with only the left side available?
example:Li + O2 →

C5H12 + O2 →

Does this require more chemistry knowledge (with chemical bonds, etc.) or am I just missing something?

What is required is a knowledge of the products that are formed:
1) Li + O2 This must be an oxidation of lithium to lithium oxide. The formula for lithium oxide is Li2O
Now write the equation:
Li + O2 → Li2O
Now balance the equation:
4 Li + O2 = 2 Li2O

2) You are reacting a hydrocarbon with oxygen. These reactions always give CO2 and H2O as products
Write the equation
C5H12 + O2 → CO2 + H2O
Now balance the equation:
C5H12 + 8 O2 = 5 CO2 + 6 H2O