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Name:  Jessica K.
Status: educator
Grade: 6-8
Location:CT
Country: N/A
Date: 5/31/2005


Question:
How does thermal energy produce a change from one state of matter to another? What is an example?


Replies:
Jessica,

First we need to distinguish between temperature and heat - it is unfortunate that in the English language these two terms are used interchangeably. Technically, temperature should be thought of as the average velocity of particles, whereas heat is the transfer of energy. There are many instances in which heat and temperature are not equally high or low. For example a cube of ice while low in temperature need quite a bit of heat to melt. The heat from a match, while high in temperature, does not provide enough heat to melt the aforementioned ice cube.

On to your question. A change of state generally means a change of phase (solid to liquid or vice-versa, liquid to gas or vice-versa). Applying heat to liquid water will cause the water to vibrate faster (go up in temperature). At 100degC and 1atm of pressure, the applied heat no longer causes a rise in temperature. Rather the energy is used to break the intermolecular forces holding the water molecules in a liquid state. Thus, the liquid particles change to gaseous particles (while still holding at 100degC). Additional heat will be used until all the water has turned to steam, at which point any more additional heat will make the steam go up in temperature.

Greg (Roberto Gregorius)



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