If we look into the past we will discover that the teachers of thermodynamics were always trying to interpret an important part of their science by using geometry. The relation between geometry and thermodynamics is of great interest and importance in teaching thermodynamics. This article examines the way undergraduate students of thermodynamics study the ideal gas case and handle its fundamental functions by using geometric objects like surfaces and common computer software. The results indicate that students find the graphical method of elaborating a fundamental function of a system efficient and easy to use. Since basic mathematics and computer skills are required, we conclude that the method is an efficient way of making not only qualitative interpretations, but also quantitative assessments of the behavior of any thermodynamic system. (Contains 8 figures and 1 note.)