Let’s look more closely at how molecules move within a
planetary atmosphere. The kinetic energy of a molecule (or
any object) is determined by its mass and its speed. When
a volume of air contains molecules with different masses,
the average kinetic energy tends to be distributed equally
among the different types. In other words, each type of
molecule, from light to massive, will have the same average
kinetic energy. This average kinetic energy of the gas
molecules is directly proportional to the temperature of the
gas (Connections 9.1). So for a gas at a given temperature,
if each type of molecule has the same average energy, then
the less massive molecules must be moving faster than the
more massive ones. For example, in a mixture of hydrogen
and oxygen at room temperature, hydrogen molecules will
be rushing around at about 2,000 meters per second (m/s)
on average, while the much more massive oxygen molecules
will be moving at a slower 500 m/s. Remember, though, that
these are the average speeds. A small fraction of the molecules
will always be moving much slower than average,
while a few will be moving much faster than average.
Let’s look more closely at how molecules move within aplanetary atmosphere. The kinetic energy of a molecule (orany object) is determined by its mass and its speed. Whena volume of air contains molecules with different masses,the average kinetic energy tends to be distributed equallyamong the different types. In other words, each type ofmolecule, from light to massive, will have the same averagekinetic energy. This average kinetic energy of the gasmolecules is directly proportional to the temperature of thegas (Connections 9.1). So for a gas at a given temperature,if each type of molecule has the same average energy, thenthe less massive molecules must be moving faster than themore massive ones. For example, in a mixture of hydrogenand oxygen at room temperature, hydrogen molecules willbe rushing around at about 2,000 meters per second (m/s)on average, while the much more massive oxygen moleculeswill be moving at a slower 500 m/s. Remember, though, thatthese are the average speeds. A small fraction of the moleculeswill always be moving much slower than average,while a few will be moving much faster than average.
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