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A burning body has flames (Candle flame)whereas a hot or warm body (warm utensil or body being hot but doesn’t burn )is just very hot. Keeping hand near a burning body makes you feel hot but not exactly near a hot body.A burning body has flames which are yellow,then blue and purple for some outside in colour.

What exactly is a burning body and how does it differ from a warm-body?

Please tell how can I improve my question if not suitable ?

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    $\begingroup$ Define a "burning body"...what are you specifically referring to? A burning wooden log? Candle flame? $\endgroup$ – M. Farooq Nov 14 '20 at 18:03
  • $\begingroup$ Yes I am referring to that. $\endgroup$ – srijan Sri Nov 14 '20 at 18:09
  • $\begingroup$ Please also tell me how did you not get my question at first instance .What is the information that is missing ? It helps me improve my posts.Thank you $\endgroup$ – srijan Sri Nov 14 '20 at 18:11
  • $\begingroup$ I feel that you should clarify what burning body you are referring to? If it is a candle flame, write candle flame. Be more specific please. $\endgroup$ – M. Farooq Nov 14 '20 at 18:21
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    $\begingroup$ Being hot is a state. Being burnt is a process of ongoing chemical reaction, usually with aerial oxygen. If there are evolving flameble gases or vapours, a flame is formed with light emitting ions, radicals and hot solid particles. If nonvolatile solid is burning, like some metals, flame does not occur, heat concentrated on the surface, reaching very high temperature with bright light, like magnesium or termite. Material can be burnt without oxidation, just by thermal decomposition. $\endgroup$ – Poutnik Nov 14 '20 at 19:27
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You're really asking about the difference between a physical change and a chemical change.*

In a physical change, the chemical identity of the substance doesn't change. In a chemical change, it does.

Suppose you take cube of sucrose (table sugar) at room temperature. If you heat it up, it will become warmer. But it will still be, chemically, sucrose. It will just be sucrose at a higher temperature. Since the chemical identity did not change, it is a physical change:

$$\ce{C12H22O11(s, room\,T) -> C12H22O11(s, warm\,T)}$$

[$\ce{C12H22O11}$ is the chemical formula for sucrose; "s" means solid, "l" means liquid, "g" means gas.]

If you warm it more (to $170 \,^\circ \text{C}$) it will melt. Melting is a physical change, because after the cube melts, it still consists of sucrose molecules; though these will now be in the liquid state:

$$\ce{C12H22O11(s) -> C12H22O11(l)}$$

But suppose you instead flow enough energy into it to break the bonds that hold the sucrose together, causing it to combust, in the present of oxygen, into water and carbon dioxide. That is what happens when it burns. This is a chemical change because, as it is happening, the sucrose and oxygen are being changed into new chemicals: water and carbon dioxide:

$$\ce{C12H22O11(s) + 12 O2(g) -> 12CO2(g) + 11 H2O(l)}$$

This chemical change releases energy, which (in this case) takes the form of heat and light (which is why it feels hot, and you can see a flame).

In sum, a warming body is undergoing a physical change. A burning body is undergoing a chemical change.

[*Yes, some might take issue with this distinction, but it is used in all first-year chemistry textbooks I've seen, indicating there is a consensus among educators in this field that this is a useful distinction for beginning students to learn.]

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    $\begingroup$ I think this might be indeed useful for the OP, that certainly is a beginner. $\endgroup$ – Alchimista Nov 15 '20 at 12:01
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Fire or flame is a luminous chemical reaction in the gas phase, i.e, such a chemical reaction is generating heat + light. Not all flames are very luminous e.g., hydrogen oxygen flame is very very light blue...hard to see.

Candle flames are yellow because of glowing carbon particles. The blue/purple color comes from small molecules formed by the decomposition of hydrocarbons emitting blue light. If you are burning wood etc., the yellow color can also come from sodium. The flames keep moving because the hot air rises around the flame.

A warm body is relatively more simple. There is no chemical reaction, that is you do not see multiple colors. A very hot body (again no chemical reaction) is a blackbody radiator. It emits a continuous spectrum. Flame spectrum is not continuous.

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  • $\begingroup$ Fire is also produced when stones are rubbed hard and their spark if put on grass , generates fire.Similarly a lighter.How does that fire get formed . So how did fire actually come ? $\endgroup$ – srijan Sri Nov 14 '20 at 19:20
  • $\begingroup$ How did that chemical reaction happen and why did it?. $\endgroup$ – srijan Sri Nov 14 '20 at 19:24
  • $\begingroup$ When you rub two stones and see sparks, that is not fire. This is a glowing piece of stone. As I said, fire is a chemical reaction in the gas phase. $\endgroup$ – M. Farooq Nov 14 '20 at 19:25
  • $\begingroup$ Also read about Flint en.wikipedia.org/wiki/Flint $\endgroup$ – M. Farooq Nov 14 '20 at 19:28
  • $\begingroup$ @robertpatrick Stone sparks are not fire, but electrostatic discharge of high voltage, because of quartz piezoelectric phenomena. BTW, think thoroughly at least an hour about each your question, and search for possible answers, before posting such a question. Writing answers about topics described in textbooks and on internet many times is wasting human resources . $\endgroup$ – Poutnik Nov 14 '20 at 19:33
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A hot or warm body stays without any change after the end of the experiment. It can be reheated over and over again. A burning body is changed into ashes at the end of the experiment. It cannot burn twice.

Edit : Answer to a comment by Robert patrick. I don't understand the following question in your comment : How is that burn produced ? Why is it yellow ? For me a burn is a mark made by a cigarette or a similar hot piece. It is brown or black. It cannot be yellow. Sorry. I don't understand. Maybe you would speak of the color of the flame. Well. The flames are not always yellow. The candle flame is yellow indeed, and this color is due to the presence of solid carbon in the middle of the flame. And carbon, as every substance heated to more than 800°C is incandescent, or white-hot, producing a yellow light. If you pass a spoon or any solid object quickly across the flame, it will be soon covered by soot (charcoal), which shows that there is some charcoal in the center of the candle flame.

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  • $\begingroup$ How is that burn produced? Why is it yellow?Why does the flame move a bit(You know like it moves a bit , for example the candle flame . It isn’t that it stays constant. $\endgroup$ – srijan Sri Nov 14 '20 at 17:10
  • $\begingroup$ I hope you get my question .@Maurice. $\endgroup$ – srijan Sri Nov 14 '20 at 17:20

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