  In order to improve the teaching of the course of statistical physics in
universities, in this article we introduce nonextensive statistics, a new
statistical theory about complex systems. We study the two modification
coefficients a and b in the van der Waals' equation in nonextensive statistics
and thus understand the possible relation between the van der Waals' equation
and the nonextensivity. We express these coefficients when a real gas is
regarded as the nonextensive gas and then relate them to the q-parameter in
nonextensive statistics. Furthermore, we derive the q-parameter of a real gas,
which contain the intermolecular Lennard-Jones potential, but also strongly
depend on the state parameter and molecular number of the gas. From the new
statistical physics, we show that the nonextensivity plays a significant role
in the coefficients of the van der Waals' equation if the gas contains limited
number of molecules or the gas is regarded as a few-body system. This article
is suitable to read for senior undergraduate students, graduate students and
teachers who teach the course of statistical physics in universities.
