College Chemistry : Combustion Reactions
Study concepts, example questions & explanations for College Chemistry
All College Chemistry Resources
Example Questions
Example Question #1 : Combustion Reactions
Suppose that the only elements a compound contains are carbon, hydrogen, and oxygen. If complete combustion of 
Note: The molecular weight of this compound is 
To answer this question, it's important to remember the details of combustion reactions. In the presence of oxygen and a sufficient amount of energy to initiate the process, combustion reactions that go to completion will result in the complete oxidation and breakdown of the initial reactant.
The 
The first step then is to use the mass of each product to find the mass of each element in the original compound. To do this, we'll need to use the molar mass for each of the products as well as the individual elements.
The combined mass of carbon and hydrogen in the original compound is 
The remaining mass will come from oxygen. Thus, the original compound will contain 
Once we have the mass of each element, we can use that information to calculate the number of moles of each element in the original compound.
Now that we have the relative molar amounts of each element in the original compound, we can find the empirical formula by finding the smallest whole number ratios.
From this, we can conclude that the empirical mass of the compound is 
Finally, since we are given the compound's molecular weight, we can use that information to find the molecular formula for the compound.
Certified Tutor
All College Chemistry Resources
