In the Newtonian universe, the one most of us live in, stuff is stuff and energy, energy. In high school we write down chemical reactions without thinking twice, or at all.
We "learn" that complete combustion gets us to water and carbon dioxide.We're more concerned with balancing these equations than we are with the reality they represent.
Here's one for burning propane:
C3H8 + 5O2 => 3CO2 + 4H2O
If you burn propane completely, you get water.
Want evidence? Grab a propane torch, light it, and sweep the flame over some cool metal--a kitchen faucet works well.
What do you see?
Yep. A flash of "fog"--go ahead, taste it. It's water.
Next time you're grilling some clams, hold your hand a bit over the fire, not so close as to fry yourself (that I even need to say as much gives me pause about our species), but close enough to feel the warmth. Your hand will "sweat" quickly.
Except it's not from you--it's water that used to be part of the coals and part of the air, molecules now rearranged into water.
I bet at least half my students can balance a combustion equation. I bet only one in a hundred grasps that water and carbon dioxide can come from scrambled up particles of propane and oxygen.
(That stuff that looks like water coming from your car's tailpipe? Yep, it's water...I once even tasted it to be sure.)