This equation tells us that, if we know the values of n, T, and V for a particular substance,
then the pressure has a fixed value. Each substance is described by its own
equation of state, but we know the explicit form of the equation in only a few special
cases. One very important example is the equation of state of a ‘perfect gas’, which has
the form p = nRT/V, where R is a constant (Section F.3). Much of the rest of this
chapter will examine the origin of this equation of state and its applications.