Definition of a Real Gas
A real gas is any gas that deviates from the theoretical ideal gas behavior. Unlike hypothetical ideal gases, real gases have molecules that occupy a finite volume and exert attractive or repulsive forces on one another. These characteristics mean real gases do not perfectly follow the ideal gas law, especially under certain conditions.
Factors Causing Deviation
The primary reasons real gases deviate from ideal behavior are the non-negligible volume of their individual molecules and the presence of intermolecular forces (such as Van der Waals forces) between them. Ideal gas models assume molecules have no volume and no interactions, but in reality, gas particles occupy space and influence each other's movement.
When Real Gas Behavior is Significant
Real gas behavior is most noticeable and significant at high pressures and low temperatures. At high pressures, gas molecules are forced closer together, making their finite volume and intermolecular attractions more pronounced. At low temperatures, molecules move slower, allowing intermolecular forces to have a stronger, more noticeable influence on their interactions.
Accounting for Real Gas Properties
To describe the behavior of real gases more accurately, modified equations of state are used. The most common example is the Van der Waals equation, which introduces specific correction terms for the molecular volume and the attractive forces between molecules, providing a better prediction of gas behavior under non-ideal conditions relevant to industrial and scientific applications.