# Homework Help: Pressure and volume graph

1. Jul 18, 2009

### intenzxboi

Just wondering on a pressure volume graph is the temperature constant??

so does that mean the the heat taken in during the process is the negative of the change in energy of the gas??

2. Jul 18, 2009

### cepheid

Staff Emeritus
Not necessarily. Look at the ideal gas law:

PV = nRT

==> P = nRT / V

This means that IF T is constant, then the PV curve is given by something that looks kind of like y = C/x. You can see that constant temperatures will therefore define a whole family of curves that look like this (they only differ in what C is). These curves are called isotherms, and the corresponding processes are isothermal. However, almost any other kind of PV curve could be allowed (representing a process in which the temperature DOES change). For instance, there are adiabatic processes (which have no net heat flow), isobaric processes (which occur at a constant pressure and therefore correspond to horizontal lines), isochoric processes (which occur at a constant volume and are therefore vertical lines), and any other curve (which doesn't necessarily fall into any of these categories).