In an experiment, 1 mol of propane is burned to form carbon dioxide and water. how many moles of oxygen are needed for the reaction?

1) Compounds:

Propane: CH3CH2CH3 or C3H8

Oxygen needed for comustion: O2

Carbon dioxide: CO2

Water: H2O

Note: any number to the right of an element is a subscript.

2) Chemical reaction:

C3H8 + 5O2 > 3CO2 +  4H2O

3) molar ratios:

1 mol C3H8 : 5 moles O2 : 3 moles CO2 : 4 moles H2O

5 moles of O2 is needed for the reaction (combustion of 1 mol of propane)