Yes.
No. Combustion is a *form *oxidation. It makes no more sense to say “Oxidation occurs at lower temperatures than combustion” than to say “Birds are smaller than crows” or “water is colder than the rain”. Just as crows are a type of bird and rain is a type of water, so combustion is a type of oxidation.
And just to really drive the point home, some non-combustion forms of oxidation occur at temperatures higher than some forms of combustion.
Edit: But I am speaking specifically of glucose and its combustion and oxidation. I guess the point raised by one user - that I’m not on fire right now - means that oxidation occurs at lower temperatures than does combustion.
More correctly, combustion is just non-self-propagating combustion. It’s perfectly possible for a combustion reaction to occur both slower and cooler than a non-combustion oxidation.
Consider a crystal of glucose that is smoldering at just a couple of hundred degrees Celsius. It’s certainly a combustion reaction, but it may takes days to complete. In contrast if you place the same amount of sugar into an inert atmosphere with a strong oxidising agent it will oxidise completely within seconds at a much higher temperature, but it won’t combust.
If the test asked “Does oxidation occurs at lower temperatures than combustion” and the correct answer was “Yes”, then sure, challenge it.
The oxidation reaction occurring in the exhaust of your typical car to remove unburned hydrocarbons occurs at temperatures ~500oC, but it sure ain’t combustion, it’s a non-self-sustaining catalysed reaction.
In contrast, many long chain hydrocarbons can smolder at temperatures below 200oC, and that is indisputably a combustion reaction.
So in no sense is it true to say that oxidation occurs at lower temperatures than combustion.
No part of you is as hot as fire.
I’d like to challenge that :eek:.
Anyway, theoreticals aside, can glucose be combusted at a temperature lower than that needed to oxidize it?
Even for glucose it won’t be true. Glucose will combust (smoulder) at around 400oC at least, possibly even lower. It can be oxidised using a catalyst at temperatures of over 1000oC. So clearly the combustion is occurring at a lower temperature than the non-combustion oxidation.
And as I pointed out, it doesn’t mean that.
This town is not on fire, does that prove that nobody in town is using a wood fireplace? Or does it prove that fireplaces oxidise wood at lower temperatures than house fires?
Or does it just prove that when you disperse an oxidation reaction throughout a huge heat sink with a good cooling system, the temperature remains low?
A fire is all oxidation reaction across the entire surface area. In contrast the oxidation reactions in your body are confined to a few tiny organelles, probably less than 1% of your total body volume, and most of the rest is water. Even if the oxidation reactions within your cells were generating *more *heat than a fire, you still woudln’t expect your body to reach anything like the same temperature.
A fire is a system that burns a mass of fuel in a small volume with a low heat capacity. You body is s system that burns the same mass fuel in a large volume with a high heat capacity.
Even if the heat yields of the reactions are perfectly equal, which system will reach a higher temperature?
I suspect that oxidation within the body does result in the result of less heat/unit time, but I wouldn’t put money on it.
To say it as an unrestricted generalization is not true, indeed, but it is true to say that very many forms of oxidation, including the oxidative metabolism of glucose within cells, take place at a lower temperature than many forms of combustion, including the combustion (whether partial or complete) of glucose. I think that is waht teh OP is asking about.
Metabolic oxidation of glucose is a multistage process designed to convert as much of that energy to ATP as possible. This is done by a series of reactions, each individually releasing a little bit of heat.
IIRC a drug was once tried that short circuited the electron transport chain (by permitting protons to flow across the membrane without driving the production of ATP. The drug resulted in a much faster release of heat - and patients came down with life threatening fevers. All because the oxidation of glucose was effectively speeded up with a more rapid release of heat.
I’m going to throw a spanner in the works here and ask:
Oxidation
Glucose + oxygen (room temp) -> carbon dioxide + water (room temp) + heat
Combustion
Glucose + oxygen (room temp) -> carbon dioxide + water (hot) + heat
Isn’t some heat used to heat the products in combustion, so less excess heat is produced?
Fascinating. Do you happen to know the name of the drug? And what is the point of the drug? Wouldn’t a reduction of ATP production only lead to lethargy?
Anyway, I think that Blake has a point - the body is 80% water and even if oxidation of glucose occurred at an extremely high temperature, the water would contain the heat. Water has a high specific heat after all.
Wel then can we see you evidence.
A question was asked. You stated that the answer was “false” based upon an argument. I pointed out that the argument was flawed. And you respond by pointing out that the answer is “false”.
That isn’t valid in any way.
Where is your evidence that the volume of the mitochondria immediately surrounding each stage of the Krebs cycle never get as hot as fire, even for a femtosecond?
Simply repeating an assertion does not make it true. Where is your evidence that it is true.
As I said, i suspect that you are correct, but I also wouldn’t be at all surprised to discover that you are incorrect. Odd things happen at the tiny scales we are speaking of. You might think that the interior of a cell could never get high enough to boil water, but if the volume is small enough, that can happen quite easily without setriment
And we still haven’t got any evidence of that one way or another. Just your flawed argument that if it were higher, we would all catch fire.
Some heat must be used to heat the products in oxidation too. Your enzymes won’t work at 5oC, the body has to use some of the heat from oxidation to heat the products to >20oC or the oxidation reaction ceases. That is what we call “freezing to death”.
In the case of both combustion and oxidation, if the ambient temperature is above that needed to sustain the reaction, no heat is added back to the reaction.
Are you nitpicking? Then what if oxidation produces gases at 100°C, but combustion produces gases at 500°C?
I don’t understand. And no, I’m not nitpicking, it’s a highly relevant point.
I’m saying the 2 processes’ products take away different energies from the reaction, so the remaining heat produced may be different. I didn’t say the reaction had to occur at 5°C or body temperature.
May I offer that oxidation can occur in a number of ways. It can be chemical (acid reaction.) It could be through the application of heat in excess of the substance’ energy of activation.
/thread (?)
Edit: the quote was from Biology by Campbell, et. al.
The oxidization of glucose is a multi-step chemical-reaction that breaks down the molecule and stores away fractions of its energy during each step of this process to be used for cellular respiration when needed. The heat created during the reactions must be lower and spread out over time, as most of the energy is stored chemically in ADP molecules to be used for cellular respiration when needed.
Taking a spoonful of sugar (no matter how pure), I gather, wouldn’t combust as completely since the higher intensity of direct heat is creating a thermal form of oxidization, there wouldn’t be an even flow of heat/oxygen to react to the sugar as thoroughly, so you’d get a mess of sooty carbon, nitrates from the air, and stuff like carbon monoxide.
Oxidization, yes. But two completely different processes/circumstances, creating two very different reactions/results.