Chemistry Project

[aznhiphopkids]

Hi i have this project for my chemistry class..

and i need help on it...

first i need to figure out how black light works.. and how those substances shows underblack light doesn't show under regular light.. i need to explain those in terms of wavelength of the light and stuff... but i don't get it...

and second i need to find out how paper is able turn in to smoke with out turning in to liquid first.. becuz i learned that solid must passed the melting point to turn to liquid and vaporate to gases from that phase..

[Tim_Lou]

Hi, welcome to our forum.

for black light information, check out this website:

http://chemistry.about.com/cs/howthingswork/f/blblacklight.htm

or you may wanna check this website about material absoptions:

http://www.shu.ac.uk/schools/sci/chem/tutorials/molspec/beers1.htm

the reason why it works is because the material absorbs the "black light", their electrons take the energy and get excited, which "jump" to a higher orbital level... almost instantly, the electrons fall back to the ground level or some other levels above, which they emit photons in a certain wavelength... if the wavelengths are those that we can see, then we can see them glowing.

 

there isnt a theory about absorption and emissions of photons of all materials... but there is one about the hydrogen atom, the Bohr Model:

http://csep10.phys.utk.edu/astr162/lect/light/bohr.html

http://www.colorado.edu/physics/2000/quantumzone/bohr.html

 

well, i dont know much... my information is very limited.

 

:hihi: turn paper into smoke? what do you mean? :rant:

do you mean sublimation or what?

[TeleMad]

and second i need to find out how paper is able turn in to smoke with out turning in to liquid first.. becuz i learned that solid must passed the melting point to turn to liquid and vaporate to gases from that phase..

 

No, a solid melting and then the liquid vaporizing into a gas is the common series, but it is not a required series. There is a process called sublimation in which a solid goes directly into a gaseous state, bypassing liquid (the opposite - a gas solidifying directly without going through a liquid state is called deposition).

 

One common example of sublimation is moth balls: they are a solid that slowly convert into a gas without ever going through a liquid state. Dry ice is another commonly mentioned example. Even the water ice in your freezer will undergo sublimation: if you make ice and then leave the ice trays alone for several weeks, then examine them, you will see that the ice has shrunk: the ice didn't turn into liquid, but straight into a gas.

 

If you look at a typical phase diagram, which shows the states of matter for a particular substance at different combinations of temperature and pressure, you will that at the lowest pressures a horizontal line can be drawn from the solid state to the gaseous state without having to pass through a liquid state, thus indicating that a phase transition can occur from a solid to a gas directly.

[Chris The Great]

I think he means burning.

 

When paper burns, it does not follow the normal melting/boiling type steps. It is a chemical reaction in which a solid is turned into a gas, and so is completely different than melting and boiling.

 

If you mean changed into smoke, smoke is not a gas. It is a suspension of small solid particles in air.

[TeleMad]

I think he means burning.

 

I think he also means ...

 

... i learned that solid must passed the melting point to turn to liquid and vaporate to gases from that phase..

 

In fact, that concept seems to be the underlying one. And it was that general, underlying concept that I addressed. For example, note that I brought up several phenomena - dry ice, moth balls, water ice, typical phase diagrams - but didn't once actually mention smoke.