# In an experiment, 1 mol of propane is burned to form carbon dioxide and water: C_3H_8 + 5O_2 -> 3CO_2 + 4H_2O. How many moles of oxygen are needed for the reaction?

Look at your stoichiometric equation.........$\text{5 moles}$ of ${O}_{2}$ are required...........
${C}_{3} {H}_{8} \left(g\right) + 5 {O}_{2} \left(g\right) \rightarrow 3 C {O}_{2} \left(g\right) + 4 {H}_{2} O \left(g\right)$
The stoichiometric equation CLEARLY specifies that $\text{1 mol}$ ($44 \cdot g$) of propane reacts with $\text{5 moles}$ ($160 \cdot g$) of dioxygen to give $\text{3 moles}$ ($132 \cdot g$) of carbon dioxide, and $\text{4 moles}$ of water ($72 \cdot g$). Clearly, $\text{GARBAGE IN EQUALS GARBAGE OUT}$, and this underlies the principle of the stoichiometry.