internal pressure

Internal pressure is the pressure within a portion of matter that arises from the attractive forces between its molecules. This concept is related to total internal energy, which is the sum of all forms of energy within a substance at a given thermodynamic state. These forms include the kinetic energy of molecules (translational, rotational, and vibrational) and the chemical energy stored in molecular bonds and interactions.12

Pressure itself is defined as the perpendicular force per unit area. For a gas, this pressure results from the constant bombardment of container walls by its molecules. Understanding internal pressure is crucial in thermodynamics, particularly when analyzing processes like gas expansion within a cylinder. Changes in internal energy are directly linked to heat absorbed and work done by the system, following the first law of thermodynamics: (\Delta U = Q - W). High pressure can significantly alter a material's physical properties, including its volume and electric conductivity.345