19.2. Molecular Kinetic Theory of a Monatomic Ideal Gas http://www.ck12.org
TABLE19.1: Table of Specific Heat Values
Substance Specific Heat,c(cal/g◦C)
Air 6.96
Water 1.00
Alcohol 0.580
Steam 0.497
Ice(− 10 ◦C) 0.490
Aluminum 0.215
Zinc 0.0925
Brass 0.0907
Silver 0.0558
Lead 0.0306
Gold∼Lead 0.0301TABLE19.2: Table of Heat of Vapourization
Substance Fusion,Lf(cal/g) Vaporization,Lv(cal/g)
Water 80.0 540
Alcohol 26 210
Silver 25 556
Zinc 24 423
Gold 15 407
Helium - 5.0Entropy
The last major concept we are going to introduce in this chapter is entropy. We noted earlier that temperature
is determined not just by how much thermal energy is present in a substance, but also how itcanbe distributed.
Substances whose molecules have more degrees of freedom will generally require more thermal energy for an equal
temperature increase than those whose molecules have fewer degrees of freedom.
Entropy is very much related to this idea: it quantifies how the energy actuallyisdistributed among the degrees of
freedom available. In other words, it is a measure of disorder in a system. An example may illustrate this point.
Consider a monatomic gas withNatoms (for any appreciable amount of gas, this number will be astronomical).
It has 3Ndegrees of freedom. For any given value of thermal energy, there is a plethora of ways to distribute the
energy among these. At one extreme, it could all be concentrated in the kinetic energy of a single atom. On the
other, it could be distributed among them all. According to the discussion so far, these systems would have the same
temperature and thermal energy. Clearly, they are not identical, however. This difference is quantified by entropy:
the more evenly distributed the energy, the higher the entropy of the system. Here is an illustration: