Heat: the Essentials
Heat, Temperature, Specific Heat, Work
The first thermometer (Galileo’s) used expansion of gas with temperature: it wasn’t
reliable because it failed to allow for atmospheric pressure variation.
Mercury in glass became the standard, and made possible the discovery of the
Zeroth Law of Thermodynamics
:
If two objects are in thermal equilibrium with a
third, then they are in thermal equilibrium with each other.
(The “third body” in a
practical situation being the thermometer.)
The
unit of heat
:
1
calorie
is the heat required to raise the temperature of 1 gram of water
by 1 degree Celsius.
BUT
the Calories labeling food items are
KILOcalories
: enough to heat one
kilogram
of
water through one degree!
The specific heat of a substance is the heat required in calories to raise the temperature of
1 gram by 1 degree Celsius.
And, you must be able to use this to solve simple calorimetric problems: finding specific
heat of a sample (as we did in class) by immersing it in boiling water for a while, then
transferring it to some cold water at a known temperature and finding the change in cold
water temperature.
Be aware of the result of Dulong and Petit, that for a whole series of elements
the product of
atomic weight and specific heat
was the same, and its significance in terms of heat capacity
per atom.
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- Fall '07
- MichaelFowler
- Work, Heat, Third Law Of Thermodynamics, Trigraph
-
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