When meat begins to smell after it sits in the hot sun for a few hours does it have a chemical reaction?

Oh, dude, you bet it does! When meat starts to stink after sunbathing for a while, that's thanks to a lovely little process called oxidation. Basically, the fats in the meat are breaking down and releasing some not-so-pleasant odors. So yeah, that funky smell is definitely a chemical reaction at play.