TABLE OF CONTENTS In kinetic theory, the composition of a gas is considered at the microscopic level. A gas is assumed to be made up of small individual molecules that are constantly in a state of motion. The name molecule can mean a single-atom molecule or a molecule with more than one atom. In each atom, a nucleus is surrounded by orbiting electrons. The internal structure of the molecule may change during an interaction with other molecules, such as collision. Collisions with other molecules occur continuously as the molecules move freely in their state of motion. Collision will also happen when a surface is present in its path. The intermolecular collision causes the magnitude and the direction of the velocity of the molecule to change, often in a discontinuous manner. If there is no collective, or macroscopic, movement, the motion of the molecule is completely random. This freedom of movement is not shared by liquid or solid molecules.
A molecular model for gas would then describe the nature of the molecule, such as the mass, the size, the velocity, and the internal state of each molecule. A measure for the number of molecules per unit volume, or number density n, would also be a parameter. The model also describes the force field acting between the molecules. The force field is normally assumed to be spherically symmetric. This is physically reasonable in light of the random nature of the large number of collisions in most cases. The force field is...
