Earth mass conversion to thermal energy

1. May 14, 2007

cliffe

Given the conceivably immense conversion of earth mass contained in fuel substances, over the past century or so, to heat or other forms of radiant energy that eventually escape into space, is there any known calculation of mass loss attributable to this phenomenon? If so, how much is it counteracted by the influx of cosmic particles, meteorites, etc.

2. May 14, 2007

cliffe

Average global oil consumption in the 1990s was in the range of 80 million bbl/day, or 29.2 billion bbl/year.

3. May 14, 2007

cliffe

1 bbl crude = approx 0.136 tonnes
1 m3 coal = 1.2 tonnes
1 million m3 methane = 605.8 tonnes

4. May 14, 2007

Staff: Mentor

The mass of the fuel isn't converted to energy and the earth is pretty closes to being in thermal equilibrium with the energy it gets from the sun. The amount of mass lost by radiation is imperceptibly small. But you can calculate the order of magnitude by using the total solar power received (174 petawatts) and applying e=mc^2

Last edited: May 14, 2007
5. May 14, 2007

cliffe

Have trouble understanding this. How much does a barrel of oil weigh after you burn it? What's the breakdown of gravity-bound remnants? MC2=E, but is E subject to gravity?

6. May 14, 2007

cliffe

Converting oil to ergs seems massively inefficient if there's so much mass left.

7. May 14, 2007

cliffe

(no pun intended)

8. May 14, 2007

Staff: Mentor

Almost exactly the same as it weighed before you burned it.
Gravity doesn't have anything to do with this. You asked about mass.

9. May 14, 2007

Staff: Mentor

Chemical reactions aren't nuclear reactions. Even in most nuclear reactions, though, there is very little conversion of mass to energy.

10. May 14, 2007

Staff: Mentor

Here's the calculation for diesel fuel, with an energy density of 45 MJ/kg:

4.5 E^7 = m* 3E^8 ^2
m=1.5 E^-9 kg

So every kg of diesel fuel burned yields 0.9999999985 kg of waste products.

11. May 15, 2007

cliffe

I meant to imply remnants other than heat and work energy resulting from the combustion, assuming that the latter are not subject to gravity. But thanks for this, Russ - it's really an eye-opener for me!

Over and out for this thread,

Cliffe

12. May 15, 2007

Danger

For comparison, an estimated 100,000 tonnes of material arrives from space every year. Our planet, she is getting fat.

13. May 15, 2007

cesiumfrog

Another point: Earth is roughly in thermal equilibrium (sunlight warms the day-surface, and the night-surface radiates heat). The chemical energy in fossil fuel (released by burning) is just solar energy, that has only been stored (underground in that chemical form) for a few ages, so on a long timescale there shouldn't be any such effect (regardless of how negligible it would be in comparison to other factors).

14. May 16, 2007

IMP

To me, a more interesting question would be: How much does the volume increase when liquid fuel is converted to a gas? If we burn a few cubic miles of liquid fuel each year, how much volume does that liquid take up when it has been converted to a gas? How much are we thickening the atmosphere?

15. May 17, 2007

mgb_phys

Simple enough to work out.
Assume liquid fuel is approx 10-Carbons , C10H22 - reasonable average of Petrol,Diesel,Kerosene
C(10)H(20) + 15O(2) -> 10C0(2) + 10H(2)0
So 1 mole of 'fuel' = gives 10moles of C02 + 10 moles of water but uses up 15 moles of oxygen, so should actually decrease the amount of atmosphere once the water condenses out.

Last edited: May 17, 2007