Students are sometimes unclear about which of the equations taught in the topic of Thermal Physics apply to ideal gases and which apply to all systems (whether ideal or real gas, even liquids and solid). The following table should help to clarify:
| Applies to Ideal Gas only | Applies to all systems | |
| Gas Laws | ||
| Average Kinetic Energy | $$ |
$$ |
| Internal Energy | ||
| First Law of Thermodynamics | applies to all systems |