Looking at the law of conservation - energy cannot be created nor destroyed; rather, it transforms from one form to another, I am left a bit confused. I understand that kinetic energy can become thermal energy, but lets say you have a campfire going, after its done all you have is ash that can't be used anymore, so what happens to the energy thats burned from the fire? Where does that energy go?
If the answer is you use the heat to power something else, isn't that energy gone once the heat dissipates? So how can energy not be destroyed?

ANSWER: Hi Mike,

The energy is not destroyed, it is dissipated to the point of being imperceptable. The heat from a camp fire is dissipated by Conduction into  the ground, by Convection to the air and by Radiation out to space. So the fire is heating up thr entire Earth. Small fire huge Earth = imperceptable change. But in theory you could measure where all the heat went as none of it is destroyed just dissipated.

I hope this helps.
Best wishes.

---------- FOLLOW-UP ----------

QUESTION: The dissipated energy is the point that confuses me. When it dissipates, how is that not the same as destroyed.. Lets say there was a sealed box filled with air and wood, then the wood is set on fire, burning all the oxygen. The sealed box would get hot inside until after the wood stopped burning. Eventually that heat would settle back down, so what happened to that energy? How would that ever be able to be used as energy for something else?
Also, not sure I fully understand the conduction, convection and radiation part. How can that energy be used for something outside the fire. If it wasn't dissipated to the point of imperceptible, how can the energy be used, hypothetically, a week from the fire itself?

Hi Mike,

Take a hot summer day with a warm breeze. Pour a small pool of water onto a plate on a table out doors.
Come back later or at intervals and the water will have disappeared.

Has the water been dissipated or destroyed?

The same if you allow a kettle to boil dry out doors.

In order to convert Heat into useful work or another form of energy a temperature difference must exist that can be exploited. As heat is dissipated and things cool down this becomes less and less possible. The heat is not destroyed but has dissipated to the point of uselessness.

I hope this helps.
Best wishes.


All Answers

Answers by Expert:

Ask Experts




Thermodynamics, chemistry, chemical reactions, kinetics, chemical reaction safety, dust explosion technology, static electricity. General science.


Over 40 years experience as a practicing thermochemist in industry. Head of the fire and explosion laboratory of a major European chemical company (Ciba-Geigy). Now retired.

Institute of Chemical Engineers. Royal Society of Chemistry.

Chartered Chemist, Member of the Royal Society of Chemistry (C.Chem MRSC). Msc Sheffield.

©2017 All rights reserved.