Energy content of gasoline and hydrogen comparative math question

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SUMMARY

The discussion focuses on calculating the energy content of gasoline and hydrogen gas. For gasoline, it is established that 1 gallon contains 2421 grams of carbon, which produces 70 grams of CO2 per megajoule of energy. The calculations reveal that 15 gallons of gasoline yield approximately 28530 MJ of energy. For hydrogen, the energy content is given as 12.8 MJ/m³, and participants discuss the necessary conversions to compare the two fuels effectively.

PREREQUISITES
  • Understanding of combustion chemistry and energy conversion
  • Familiarity with units of measurement, specifically gallons and cubic meters
  • Knowledge of molecular weights, particularly for carbon and CO2
  • Ability to perform ratio and proportion calculations
NEXT STEPS
  • Research the heat of combustion for various fuels, including octane and hydrogen
  • Learn how to convert between gallons and cubic meters for fuel measurements
  • Study the molecular weights of common elements involved in combustion reactions
  • Explore the environmental impact of CO2 emissions from different fuels
USEFUL FOR

Students in chemistry or environmental science, engineers in the automotive industry, and anyone interested in fuel efficiency and energy content comparisons.

  • #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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