Energy content of gasoline and hydrogen comparative math question

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Homework Help Overview

The discussion revolves around calculating the energy content of gasoline and hydrogen gas, specifically comparing the energy produced by 15 gallons of gasoline with that of an equivalent volume of hydrogen gas. The problem involves understanding combustion energy and the relationships between mass, energy, and carbon dioxide production.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • Participants explore the heat of combustion for gasoline, considering octane as a surrogate and discussing the carbon content in gasoline. There are attempts to relate carbon mass to CO2 production and energy output, with questions about how to connect these relationships effectively.

Discussion Status

Participants are actively engaging with the problem, questioning assumptions about the relevance of CO2 production to the energy calculations. Some have provided guidance on how to approach the calculations, while others express uncertainty about the connections between the various ratios and how to set up the calculations properly.

Contextual Notes

There is a focus on the importance of units and the need for clarity in the relationships between carbon mass, CO2 production, and energy content. The discussion also highlights the challenge of integrating multiple ratios to arrive at a solution.

  • #31
haruspex said:
Yes, you haven't used the final ratio: 70g CO2 corresponds to 1MJ energy.
If 1 gal gasoline releases 133,155 g of CO2, and each 70g CO2 indicates 1MJ of energy, how many MJ for the whole gallon?

When I did this I got 1902.214 MJ. Is this right?

If so how would I go about doing part B?
 
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  • #32
Wait I realized that is only for 1 gallon so I got 28530 MJ
 
  • #33
courtneywetts said:
When I did this I got 1902.214 MJ. Is this right?
that is only for 1 gallon so I got 28530 MJ
Right!
If so how would I go about doing part B?
This is much easier. you have 15 gals at 12.8 MJ/m^3.
 
  • #34
haruspex said:
Right!

This is much easier. you have 15 gals at 12.8 MJ/m^3.

I don't understand what this means though? Is this all the information I need?
 
  • #35
courtneywetts said:
I don't understand what this means though? Is this all the information I need?
The only other information you need is how to convert US gallons to m3. Look it up.
 
  • #36
haruspex said:
Yes. So you have, for burning gasoline:
  • 12 atomic masses C corresponds to 44 atomic masses CO2
  • 70g CO2 corresponds to 1MJ energy
  • 1 gallon gasoline corresponds to 36,315 g C
So how many J energy correspond to 1 gallon gasoline?

This is incorrect. According to the attachment in Post #4, 1 gallon of gasoline has a carbon content of 2421 g, not 36,315 g. The latter figure is for 15 gallons of gasoline.
 
  • #37
SteamKing said:
This is incorrect. According to the attachment in Post #4, 1 gallon of gasoline has a carbon content of 2421 g, not 36,315 g. The latter figure is for 15 gallons of gasoline.
Well spotted - thanks. But fortunately courtneywetts used the right ratio later.
 

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