http://www.ck12.org Chapter 13. States of Matter
FIGURE 13.5
A distribution of molecular kinetic ener-
gies as a function of temperature. The
blue curve is for a low temperature, while
the red curve is for a high temperature.At a given temperature, the particles of any substance have the same average kinetic energy. At room temperature,
the molecules in a sample of liquid water have the same average kinetic energy as the molecules in a sample of
oxygen gas or the ions in a sample of sodium chloride.
You can see an exciting demonstration of the relationship between kinetic energy and temperature by watching a
piece of nitrocellulose ignite from the compression of air at http://www.youtube.com/watch?v=jsQlfxdZ9ys.
You can visualize the motion of gas molecules indirectly by watching glass beads move in mercury gas at http://w
ww.youtube.com/watch?v=26dAsmFWz24.
Absolute Zero
As a sample of matter is continually cooled, the average kinetic energy of its particles decreases. Eventually, one
would expect the particles to stop moving completely. Absolute zerois the temperature at which the motion of
particles theoretically ceases. Absolute zero has never been attained in the laboratory, but temperatures on the order
of 1× 10 −^10 K have been achieved. The Kelvin temperature scale is based on this theoretical limit, so absolute zero
is equal to 0 K. The Kelvin temperature of a substance is directly proportional to the average kinetic energy of the
particles of the substance. For example, the particles in a sample of hydrogen gas at 200 K have twice the average
kinetic energy as the particles in a hydrogen sample at 100 K.
You can learn more about the relationship between average kinetic energy and temperature at http://www.grc.nasa.
gov/WWW/k-12/airplane/temptr.html.
You can view a simulation of the molecular motion of gas molecules as heat is added at http://www.dlt.ncssm.edu
/core/Chapter11-Thermochemistry/Chapter11-Animations/KineticEnergy-Gas.html.
Lesson Summary
- The kinetic-molecular theory describes all matter, but it is especially useful for explaining the behavior of
gases. Gas particles are assumed to occupy an insignificant volume compared to the space between particles.
Particles undergo random linear motion and collide elastically with one another and with their container. - Gas pressure results from the collisions of gas particles with an object. Pressure is measured with a barometer