Burning vs Heating:

Schaumburg, Carl                     Von Steuben High School
                                     588-2370
                          

Objectives:

To teach the concepts of chemical and physical changes, and the 
differences between burning and heating 

Apparatus Needed:

Burner, matches, wood splints, thin glass rods, Mg ribbon, candles, 
lead strips, steel wool, evaporating dish, forceps, flask, fire proof 
trivet, lighter fluid 

Recommended Strategy:

    First hold a wooden splint in a burner or torch flame.  Remove the 
splint from the flame and ask the students what is happening.  
Responses might include: smoke, wood is getting smaller, turning 
black, etc.  Hold an evaporating dish in the flame and note the soot 
on the bottom of the dish.  The point is to have the class realize 
that something is happening to the wood, new substances are being 
formed, and that the process is named burning. 
    Next hold a piece of glass tubing or rod in the flame.  Is this 
heating the same?  Does the "flame" remain when the glass is removed 
from the torch or burner flame?  Is the glass getting smaller?  Is it 
turning black, etc?  If the glass bends, simply straighten it, and 
point out that this kind of change is not permanent.  Does this 
"flame" produce the same soot as noticed with the wood?  Is this 
another example of burning or something different?  Now would be a 
good time to introduce and define chemical and physical changes. 
    Continue the process with heating of a candle halfway down the 
length of the candle (with a flame on the slant) and also in the 
usual place at the wick.  Go through the same ideas introduced in the 
previous sections and determine if the change is chemical or physical, 
heating or burning.  Other materials that could be heated are: Mg 
ribbon (be careful of the intense light), a coat hanger wire (after 
removing the paint), a strip of lead (heat over the trivet), steel 
wool, and an icicle.  Each time go through the same determination of 
the type of heating.  
    To complete the lesson, make water appear to burn.  Before class, 
add a few drops of lighter fluid to a flask.  Swirl around to 
distribute the liquid to the glass walls.  Discard the excess so that 
the flask appears empty.  Ask if water burns.  Add water to the flask 
directly from the faucet, filling to the top of the flask.  The lighter 
fluid will float to the top and can be made to burn.  End the lesson 
just at the bell and leave the "burning" water as the conclusion.  
Explain next time.