provided that there are no phase changes. [P7.3]
is: a gas that actually exists, in contrast to an ideal gas, which does not. [P7.2]
generally is: a complicated system. [P7.3]
but usually can be modelled: at low pressure, by the equation of state of an ideal gas provided that there are no phase changes. [P7.3]
often is modelled: by equations of state which allow for the undoubted facts that atoms or molecules in a gas interact and have volume. [P7.3]
Copyright 1997, The Open University