Complete Combustion - which hydrocarbon will consume more O2

In summary, the equation for part C states that there is 0.1136 moles of oxygen needed to combust 1 gram of propane.
  • #1
RoboNerd
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Homework Statement


one gram of each of the following gases is introduced into a 10 L container at 25 degrees C

a) propane
b) ethane
c) methane
d) pentane

which gas will consume the greatest mass of oxygen upon complete combustion?

The solutions says that the right answer is D. I do not know why

Homework Equations


no equations. just chemical ones.

The Attempt at a Solution



My logic is that if I have greater number of moles of hydrocarbon, I will need more oxygen to consume.

I thus thought that since methane has a lesser molar mass, we have greater moles, so we will need greater moles [which leads to a higher mass] of O2 gas needed.

Could anyone please advise on how to solve this?

Thanks!
 
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  • #2
Start with writing out balanced chemical equations for the complete combustion of each of these hydrocarbons.
 
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  • #3
OK.

My equations are as following
  • propane: C3H8 + 5O2 --> 3CO2 + 4H2O
  • ethane: 2C2H6 + 7O2 ----> 4CO2 + 6H2O
  • CH4 + 2O2 ---> Co2 + 2H2O
  • C5H12 + 8O2 ----> 5CO2 + 6H2O
I believe these equations are correct. right?

I just did some stoichiometry with approximate values, and I got 0.111 moles of O2 needed to combust the hydrocarbon in answer D.

My other calculated numbers are:
a) 0.1136 mol O2 needed
b) 0.1167 mol o2 needed
c) 0.125 mol o2 needed
d) 0.111 mol o2 needed.

So far, it seems that the hydrocarbon in answer d does not have the maximum need for O2 moles.

Could I have made an algebraic error?

For example, a sample calculation for my number for part A is:

(1 g C3H8)/(44 g C3H8) * ( 5 mol O2 / 1 mol C3H8) = 0.1136.

I could be wrong.

Please advise and thanks for your help!
 
  • #4
I did the calculations as well and got the same numbers as you. The answer should be C (methane), and the book is probably wrong.
 
  • #5
Wow. This seems really strange.

Thanks so much for the help!
 

Related to Complete Combustion - which hydrocarbon will consume more O2

1. What is complete combustion?

Complete combustion is a chemical reaction that occurs when a hydrocarbon (a compound made of carbon and hydrogen) reacts with oxygen to produce carbon dioxide and water. This reaction is complete because all of the fuel is converted to these end products.

2. How does complete combustion differ from incomplete combustion?

Incomplete combustion occurs when there is not enough oxygen present for the hydrocarbon to completely react. This results in the production of carbon monoxide and/or soot, which are harmful byproducts.

3. Which hydrocarbon will consume more oxygen during complete combustion?

The amount of oxygen consumed during complete combustion depends on the specific hydrocarbon being burned. Generally, hydrocarbons with longer carbon chains will require more oxygen to completely react compared to hydrocarbons with shorter carbon chains.

4. Why is complete combustion important?

Complete combustion is important because it is the most efficient way to produce energy from hydrocarbons. It also produces fewer harmful byproducts compared to incomplete combustion, making it better for the environment and human health.

5. How can we ensure complete combustion occurs?

To ensure complete combustion, it is important to have a sufficient amount of oxygen present. This can be achieved by properly adjusting the air-to-fuel ratio in a combustion system. It is also important to have proper ventilation to allow for the adequate supply of oxygen.

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