Thermodynamics Chapter 18

Thermodynamics is… The study of heat and its transformation to mechanical energy. The science of thermodynamics was developed in the 19th century, before the atomic and molecular theory of matter was understood.

The foundation of thermodynamics The conservation of energy The fact that heat flows spontaneously from hot to cold

Thermodynamics provides the basic theory of heat engines From steam turbines to nuclear reactors To the basic theory of refrigerators and heat pumps

Absolute Zero

Temperature… In principle there is no upper limit to temperature As thermal motion increases a solid melts, then vaporized, then eventually will become a plasma.

However, there is a definite limit to how cold something can be. What is absolute zero? Where does that number come from?

In the 19th Century Experiments Found… That all gases, regardless of their initial pressures or volumes, change by 1/273 of their volume of 0C for each degree Celsius change in temperature, provided the pressure is held constant. So if a gas at 0C were cooled down by 173C, it would contract according to this rule by 273/273 of its volume and be reduced to zero. Therefore a gas in a container of fixed volume cooled to 273C below zero would have no pressure whatsoever.

When atoms and molecules lose all available kinetic energy, they reach absolute zero of temperature Remember that temperature is a measure of the kinetic movement of atoms and molecules. If no more energy can be extracted from a substance, then no further lowering of its temperature is possible.

The Kelvin Scale The absolute temperature scale Named after 19th Scottish physicist William Thomson, the 1st Baron Kelvin