[Archive!] Pure mathematics, physics, chemistry, etc.: brain-training problems not related to trade in any way - page 466
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I'm going to google who Trachtenberg is.
All other conditions are identical. Humidity, density, oxygen content, etc. And even their difference does not affect the speed of the reaction as much as the heat removal from the reaction zone.
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In short, there is a famous principle of le Chatelier in chemistry: any influence on the chemical reaction shifts the chemical equilibrium in such a way as to reduce this influence. Let's write down the combustion reaction (it is exothermic):
Source fuel + Oxygen <-> Products of combustion + Heat Q
Now we will cool down the combustion zone. In other words, we will dissipate the heat. The reaction, according to the Le Chatelier principle, will align the equilibrium so as to minimise the external influence (heat extraction). It will 'tend' to generate more heat. Since we have heat on the right side of the reaction, the equilibrium will shift to the right. The fire will intensify.
And why is a fire extinguished with carbon dioxide? It's simple: carbon dioxide is one of the products of the combustion reaction. If we artificially increase its concentration, the equilibrium of the combustion reaction will shift to the left (to where there was no carbon dioxide yet), i.e. in the direction opposite to combustion.
Another example, the last one about fire: if the combustion products are removed from the combustion zone, the burning will be more intense (the reaction resists and tries to compensate for the external influence by adding more combustion products). This seems to be used in metallurgy.
I remember reading about our polar explorers who managed to survive a fire on the Vostok in Antarctica during the winter. The frost during the fire was very hard. The polar explorers recall that aluminium was burning. This does not prove anything, but it demonstrates that cold air does not prevent a fire from being very strong at all.
Theoretically the answer looks right, but I get the feeling that "heat dissipation" without taking air density into account doesn't seem quite right :)
And if the experiment is carried out in a closed vessel, to fulfill the identity of all "other conditions"? I think it's unlikely that the fuel would manage to burn faster at lower temperatures.
All other conditions are identical. Humidity, density, oxygen content, etc. And even their difference does not affect the speed of the reaction as much as the heat removal from the reaction zone.
_____________________________
In short, there is a famous principle of le Chatelier in chemistry: any influence on the chemical reaction shifts the chemical equilibrium in such a way as to reduce this influence. Let's write down the combustion reaction (it is exothermic):
Source fuel + Oxygen <-> Products of combustion + Heat Q
Now we will cool down the combustion zone. In other words, we will dissipate the heat. The reaction, according to the Le Chatelier principle, will align the equilibrium so as to minimise the external influence (heat extraction). It will 'tend' to generate more heat. Since we have heat on the right side of the reaction, the equilibrium will shift to the right. The fire will intensify.
I strongly disagree with the wording :) After all, heat will not arise from the void - in fact the influx of air/oxygen will intensify, due to faster displacement of hot air by colder air - density difference. Accelerated the oxygen inflow -> accelerated the reaction rate, rather than "taking heat away" -> accelerated the reaction rate.
You can't accelerate the oxygen in a closed vessel - it's already all there.
Victor, I was educated in microelectronics technology, I studied at the physics and chemistry department of MIET (in Zelenograd). They gave us a lot of chemistry, thermodynamics, physical chemistry, surface physics, etc. Now many things have been forgotten, but at that time our heads were puffed up from all these extensive/intensive parameters and partial derivatives in physics.
On a qualitative level, the Le Chatelier principle works well - if you control the logic and do not go beyond reasonability in reasoning. Of course, it does not explain everything (because it is qualitative), but it gives a qualitative explanation for a 1-2 year student in which direction the reaction will go when a certain action is taken.
At the quantitative level, it is described by physic chemistry. This is the same thermodynamics, only with chemical potential taken into account. But this was not the 2nd year...
P.S. There are logical flaws in your reasoning. Yes, heat does not arise from emptiness; it arises from the chemical reaction itself. If you mix sodium and water, where does the heat come from? And it is the removal of heat in the fire example that is the main reason the fire is exacerbated. The beauty of the principle is precisely that it allows you not to go into detail and predict the direction of the process immediately.
P.P.S. I might be wrong, but in exothermic reactions used in metallurgy, it is the cold oxygen that is fed to the combustion zone. Not because it is easier, but because the Le Chatelier principle works: the reaction is accelerated for two reasons at once - both by feeding external oxygen and by the fact that it is cold!
P.P.S. I may be wrong, but in exothermic reactions used in metallurgy, the oxygen in the combustion zone is cold. Not because it is easier, but because the Le Chatelier principle works: the reaction is accelerated for two reasons at once - both because of external oxygen supply and because it is cold!
Victor, I was educated in microelectronics technology, studied at the physics and chemistry department of Moscow Institute of Electronic Technology (in Zelenograd). We were given a lot of chemistry, thermodynamics, physical chemistry, surface physics, etc. Now many things have been forgotten, but at that time our heads were puffed up from all these extensive/intensive parameters and partial derivatives in physics.
On a qualitative level, the Le Chatelier principle works well - if you control the logic and do not go beyond reasonability in reasoning. Of course, it does not explain everything (it is qualitative), but it gives a qualitative explanation for a 1-2 year student in which direction a reaction will go when a certain action is taken.
On a quantitative level, this is described by physicochemistry. It's the same as thermodynamics, only with the chemical potential taken into account. But this was not the 2nd year...
P.S. There are logical defects in your reasoning. Yes, heat does not arise from a void; it arises from the chemical reaction itself. If you mix sodium and water, where does the heat come from? And it is the removal of heat in the fire example that is the main reason the fire is exacerbated. The beauty of the principle is precisely that it allows you not to go into detail and predict the direction of the process immediately.
P.P.S. I might be wrong, but in exothermic reactions used in metallurgy, it is the cold oxygen that is fed to the combustion zone. Not because it is easier, but because the Le Chatelier principle works: the reaction is accelerated for two reasons at once - both by feeding external oxygen and by the fact that it is cold!
I do not argue with the Le Chatelier principle, but I do not like the details of the solution of the problem :) I.e. it seems that the wording of the problem is such that only the Le Chatelier principle is remembered, without unnecessary details.
Nah, Alexey, don't get any funny ideas. The reaction is already steadily going on, the fire is blazing. And at the moment of Ch, we sharply cool the outside temperature - say, to -150 (let oxygen remain a gas). The layman, of course, will think that the fire will go out of action. But we are armed with Le Chatelier principle...
This is also supported by the fact that, as you correctly said, the oxygen is fed into the furnace cold - but it's not specially cooled, for example to -50 degrees (or am I wrong?).
Why not do it on purpose?
VictorArt: I.e. apparently the wording of the problem is such that only the Le Chatelier principle is recalled, without extra details.
Exactly, Victor! I did not report any additional, specific data. Well, the means to solve the problem should be chosen accordingly...
I'm slowing down, give me a formula.
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There is a set of characters. The number of characters is 2 * N, i.e. even.
Characters are divided into 2 subsets of N characters each. Determine the number of possible ways to divide symbols into subsets. The position of the symbol in the subset is not important.
That is:
1) For set {A,B} (i.e. with N=1) there is a single division option: {A} + {B}
2) For the set {A,B,C,D} (i.e. for N=2) there are 3 variants:
{AB} + {CD}
{AC} + {BD}
{AD} + {BC}
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How to determine the number of choices for an arbitrary value of N ?
First, about oxygen. Oxygen is obtained by distilling air. Although there are more modern technologies - membrane technology, for example, but it is not on an industrial scale. There is no reason to heat it. It will be heated by itself in an autogene.
Now about Na. Who said that sodium can't be mixed with water without a reaction? You can if the water and sodium are in solid form. In solid form, they don't react with each other. Think of effervescent aspirin tablets where acetylsalicylic acid and citric acid are mixed with sodium bicarbonate. Once in water - reaction, in dry form - no reaction.
Now for the reaction rate. Well, of course, the rate of reaction depends on the temperature. The higher it is, the higher it is. But let's remember the physical chemistry. What else does it depend on? Concentration. And concentration depends on what? Density, for example. I'm talking about gases. Density, by the way, is inversely proportional to temperature. So, as temperature increases from this point of view, concentration of initial substances decreases.
One more point. The reaction rate depends on the concentration of combustion products. The higher concentration of combustion products is, the lower reaction rate is.
So, the question is not very "linear". And it will be "rambling" on this forum and there will be no concrete answer.
As for me, I, too, can not give a definite answer. On the one hand I know that the reaction rate increases with increasing temperature, on the other hand it decreases (and there are examples of its use in engineering, particularly in space). The combustion process is 'auto-balanced'. That's why we're all here and not there yet .....
One more thing. What is burning? Wood, for example? Don't forget that wood decomposes when it burns: coal, methane, methanol, acetic acid, water, ash, etc. Sometimes it takes energy to decompose, and sometimes it 'self-decomposes' - depends on what is burning. There are more interesting things - a substance can be oxidised and reduced at the same time. How? Like this. The products of "combustion" also become more, but this is an illusion :)