1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What is burning and how occured heat and light

  1. Jan 25, 2013 #1
    how occur burning namely when something burn... what is the event in atomic size. atom can not burn what is burning and how occured heat and light ...is heat vibration of the atoms ??
     
  2. jcsd
  3. Jan 25, 2013 #2
    Here's an explanation by Richard Feynman

     
    Last edited by a moderator: Sep 25, 2014
  4. Jan 25, 2013 #3
    Burning is a chemical reaction that occurs between the material involved and the oxygen from the atmosphere. The oxygen molecules combine with the molecules of the material, and form new compounts (such as CO2) as well as giving off infrared and visible radiation. During the reaction, chemical bonds are broken and new bonds formed.
     
  5. Jan 27, 2013 #4
    thanks for your answers...I understand how occur burning...and so how we feel the heat ...is heat atoms of vibration and when this vibration increase and hit us so we feel that like its heat.
     
  6. Jan 27, 2013 #5

    Drakkith

    User Avatar

    Staff: Mentor

    Heat, as a general definition, is energy transferred from one body to another by thermal interaction. Transferring heat to something increases one objects temperature, and temperature is a measure of the internal energy of an object. This internal energy takes the form of molecular and atomic vibrations, rotations, oscillations, etc.

    When you put your hand over a flame you have a couple of things happening. First, the air surrounding the flame is being drawn in, thanks to convection, and heated up from the combustion process itself. This warmer air rises, which fuels the convection process that draws more air in. As the warm air rises it comes into contact with your hand and through collisions between the air molecules and your hand's molecules heat is transferred to your hand, warming it up.

    Second, the hot air and fuel itself puts out thermal radiation. Thermal radiation is EM radiation that is emitted when any object is at a temperature above 0 kelvin, aka absolute zero. The hotter an object is, the more energy it puts out as radiation and the higher frequency that radiation is. A flame typically puts out a lot of radiation in the infrared range of the spectrum, so when you put your hand over the flame you are also absorbing infrared radiation from the flame in addition to feeling the warm air. This thermal radiation is the reason you feel warm when you sit close to a fire.

    http://en.wikipedia.org/wiki/Heat
    http://en.wikipedia.org/wiki/Thermal_radiation
    http://en.wikipedia.org/wiki/Radiant_heating
     
  7. Jan 28, 2013 #6
    Yes indeed, combustion is fast oxidation. But there is an important detail: usually there is flame. Flame is more than just a hot gas with quickly moving particles, it is plasma, whose visible and IR emission is due to atomic transitions.
     
  8. Jan 28, 2013 #7

    Drakkith

    User Avatar

    Staff: Mentor

    I don't think that's true.
    See this link: http://www-spof.gsfc.nasa.gov/Education/FAQs7.html#q97

    Excerpt:

     
  9. Jan 29, 2013 #8
    Dear Drakkith,

    Thanks for helping me to analyze in more depth the subject. I might have exaggerated the importance of plasma especially in common low-temperature flames, whose light I agree should be mainly due to incandescent aerosol particles formed by incomplete combustion. However, there is no particular threshold for a gas to exhibit plasma behaviour and undoubtedly even a candle flame (T around 1000ºC) contains a small fraction of ions, and a properly conducted experiment will demonstrate it (see e.g. http://www.youtube.com/watch?v=a7_8Gc_Llr8&feature=youtu.be&hd=1 ; I have seen somewhere also a low-voltage variant, so you can not say that ionization is due to the high field). Anyway, part of the light especially in high temperature flame is due to electronic transitions, occurring not necessarily only in ions, but also in atoms and molecules.
     
  10. Jan 29, 2013 #9

    Drakkith

    User Avatar

    Staff: Mentor

    Sure, as electronic transitions don't need to occur only from a plasma. If you excite the electron to an energy level, and it stays bound to the atom, it will drop back down if it can and emit light. I believe that is the entire reason some things burn certain colors.
     
  11. Jan 29, 2013 #10
    Modern classic:
     
    Last edited by a moderator: Sep 25, 2014
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook