Molecular Motion and Collisions

Molecular Motion and Collisions

  • Molecular motion is the movement of particles in a substance caused by the energy they possess. These particles can be atoms, molecules or ions.

  • There are three types of molecular motion: translational (where the particles move from one place to another), vibrational (where particles vibrate back and forth), and rotational (where particles spin around).

  • In solids, motion of particles is primarily vibrational because particles are tightly packed together and cannot freely move around.

  • Higher temperatures lead to increased molecular motion. If a substance is heated, the energy of its particles increases, leading to more active and intense motion.

  • Collisions between molecules are a fundamental concept of the kinetic theory.

  • In a perfect gas, it is assumed that the collisions between particles are perfectly elastic, meaning the total kinetic energy of two particles before the collision is equal to the total kinetic energy of those particles after the collision.

  • In reality, some of the kinetic energy is transferred to potential energy in the system or lost as heat, and so collisions in real gases are not perfectly elastic.

  • The Law of Conservation of Momentum states that the total momentum of a system of particles is conserved unless acted upon by an external force. This principle applies to molecular collisions.

  • Pressure of a gas is caused by the momentum change of molecules when they collide with the walls of the container holding them. More collisions per unit area or higher collision energy lead to increased pressure.

  • Changes in volume, temperature or number of particles may change the pressure of a gas, as indirectly it affects the number of collisions with the container or the kinetic energy of each collision.

  • When two particles collide, they will generally move off in different directions after the collision. This randomenss of direction is due to the microscopic chaos of molecular motion.

  • Understanding molecular motion and collisions supports the understanding of many broader physics topics, including heat, thermodynamics, and gas behaviour.