Reply To: 2 Questions about burning wood & matter vs mass
Thank you for your questions. They show good thinking.
Why can’t we “un-burn” a piece of wood?
Reese is quite right in his thinking. The formula for any chemical reaction can be written backwards as well as forwards, making it theoretically possible. Specifically the chemical reaction for burning wood (mostly cellulose) is:
C6H12O6 + 6O2 —–> 6H2O + 6CO2 + release of energy
The reverse (unburning) is:
6H2O + 6CO2 + input of energy —-> C6H12O6 + 6O2 and is theoretically possible. In fact, plants do this with the aid of light energy. It is called photosynthesis.
However, distinguish theoretical possibility from practical feasibility. Plants accomplish the unburning of wood (photosynthesis) through a dozen or more individual chemical steps driven by energy from light. To have it happen on one big step as occurs in the burning is what is impossible.
Its a little like smashing a dinner plate on the floor. You can see the smashing apart occurs with one bang. You can see that the pieces might go back together to “unbreak” the plate. Then you might do so by carefully picking up each piece and fitting and glueing them back together. What remains impossible is having them go back together in one “bang.” Thus we say that the breaking of a plate (and unburning wood) are irreversible.
Is there conservation of mass as well as conservation of matter?
Yes! (But don’t confuse mass and weight.) Since each particle (atom) of matter has a certain mass and atoms remain the same, mass will also remain the same. Seeing this in practical way is what is difficult. Note from the above equation for burning wood, the major products are carbon dioxide and water (vapor) which go off in the air. (They retain their mass although weighing them is impractical.) A very small portion of the log ends up as ash. To prove that mass (in terms of weight) remains constant, you would have to burn the wood plus sufficient oxygen in a totally sealed container so that the water vapor and carbon dioxide are held in. (Scientists have done this.) It is found that the total mass and weight
does not change.
Please question more as you wish.