Is chemical combustion an exothermic or endothermic reaction?

Factual Questions
1

Example C6H12 + O2 —> CO2 & H20

Is this endothermic or exothermic.

On one hand, it releases energy in the form of heat so its exothermic, but at the same time it seems like anabolism (H20 & CO2 are formed) so it seems endothermic, as anabolism is endothermic. then again C6H12 is broken down, so it would be exothermic.

Anyone know.

2

It is exothermic.

3

All that matters is whether the reaction evolves or absorbs heat. As this reaction evolves heat, it is exothermic.

BTW, your chemical equation is not balanced.

Also, anabolism is the “general term for the synthesis of cell structures.” I don’t believe the production of water and carbon dioxide would be properly characterized as “anabolisim.”

4

An exothermic reaction releases heat. An endothermic reaction requires heat. The best way to conceptualize it IMO is think of which side of the equation has heat on it.

given X and Y, two elements

X + Y -> XY + heat
would be exothermic

X + Y + heat -> XY
would be endothermic

5

Robby’s right. The reaction you gave us is the general equation for aerobic respiration which is a catabolic process. It’s the breakdown of glucose. Water and carbon dioxide are waste products that are excreted.

6

Here’s a great website that summarizes anabolism, catabolism, etc…
http://www.bact.wisc.edu/microtextbook/Metabolism/Anabolism.html

7

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8

Not quite. He has C[sub]6[/sub]H[sub]12[/sub] , not C[sub]6[/sub]H[sub]12[/sub]O[sub]6[/sub]. If my memory of chemistry nomenclature can be trusted, that’s hexene (although we can’t tell what isomer from the formula). The diagram would be something like


  H H H H H H
  | | | | | |
H-C-C-C=C-C-C-H
  | |     | |
  H H     H H

except that the double bond could between any two carbon atoms. Alternately, it could be a ring, with all single bonds.

Wesley, generally in anabolism you’re using water and CO[sub]2[/sub] to make something more complicated. Getting water and carbon dioxide out is not anabolism.

9

You’re right, Chronos, too many years of having that same equation driven into made me see glucose instead of hexene(which it is)
-Lil

10

Nitpick: I know what you said, but just to be clear, an exothermic may often require heat as well iirc. Something like wood + oxygen + little heat -> water + co2 + lots of heat.

11

You’re thinking about activation energy. In any event, the heat represented in Moo’s equation(s) is net heat.

12

I didn’t go too far in chemistry study. Is it true that exothermic reactions work better if the ambient temperature is lower? and conversely that endothermic reactions work better at a higher ambient temperature? Because in these cases heat transfer with the environment is better.