Is carbon dioxide combining with water in cells of green plants endothermic or exothermic?

Answer 1

endothermic. it absorbs the energy of the sunlight in the leaves of the plant cells, and breaks apart carbon dioxide and dihydrogen oxide (water), and recombines the atoms into O2, and Carbon and Hydrogen and also some of the oxygen go on to form more plant tissues, or sugar, which is a 'carbohydrate'

Overall, when the atoms of water are held together, they are held together more strongly than in plain Hydrogen (H2), and plain Oxygen(O2), which are held together more weakly, but still are attracted together to a good extent, because, if they weren't, they would be floating around as free unattracted atoms.

when you bust apart atoms that were not held together very strongly in the first place, you dont need to invest a lot of energy.

now, if they recombine with new partners, like hydrogen and oxygen coming together, they attract more strongly, and like two people rushing towards each other, they will crash into each other, and if they were like bouncy balls, they would rapidly hit and bounce away, then be attracted, and bounce away, and all that vibrating sends out its energy as electromagnetic radiation, since the plus and minus charges that form the atoms are getting jostled around.

so since the two bouncing atoms are sending out their energy as electromagnetic radiation as they bounce, soon they settle down and stay tightly stuck together.

But in the process, they gave off energy, in the form of EM (electromagnetic energy), or simply by bumping into an innocent neighgoring atom, its' violent bouncing around can cause a neighboring molecule, of say H2 ,to be knocked apart, or at least stretched far apart enough so that an Oxygen that is also gotten shaken up, well that allows the original partners to be shaken away from each other enough, so that a new atomic partner can get itself close enough for the two new partners to discover they are crazy about each other, and latch on to each other, and giving up their original partners.

An so, that is how gasoline burns rapidly in a car engine, or a balloon fillled with hydrogen can burn with Oxygen. The combining of the new partners releases 'heat' or energy, which can help continue the reaction, for more and more of the molecules to recombine into new partners. This is exothermic.

but with endothermic, the process has to wait for an outside energy source to stretch the two partners of a strongly attracted molecule, such as water, to stretch those bonds loose, so they can be put with new partners that don't hold onto each other as strongly as before, but are still satisfying to the atoms, if they had feelings.

Imagine a couple of marbles that have rolled into a ten foot hole. you would have to invest the energy to lift the marbles ten feet. now if you then dropped them into a one foot hole, they would still stay close together in their new hole, but you see they are storing energy, which is an endothermic process.

so water is like the atoms, being tightly attracted, are in the ten foot hole analogy,

and the Hydrogen (H2 - two hydrogen atoms stuck together) and Oxygen(O2 - two Oxygen atoms stuck together) are when the atoms are in the one foot hole.