Kinetic theory of gases
Kinetic gas theory (formerly also dynamic gas theory) is a branch of statistical mechanics.
The kinetic theory of gases explains the properties of gases, in particular the gas laws, by the idea that gases consist of a very large number of small particles (atoms or molecules) that are in constant motion (Gr. κίνησις kínesis "motion"). The theory leads to a microscopic explanation of the properties of temperature and heat, which in thermodynamics are defined by their macroscopic properties.
As early as the 17th century, physicists such as Francis Bacon suspected that heat was a form of motion. The first to devise a more complete theory was Daniel Bernoulli in 1738, followed by Mikhail Vasilyevich Lomonosov, Georges-Louis Le Sage, John Herapath and John James Waterston, among others, but their considerations were largely ignored. It was not until 1860 that the kinetic theory of gases gained wider recognition through the work of physicists such as Rudolf Clausius, James Clerk Maxwell and Ludwig Boltzmann. At the same time, however, the kinetic theory of gases was fiercely contested, even into the 20th century by Ernst Mach and Wilhelm Ostwald, among others, because it depended entirely on the existence of atoms or molecules, which was considered a hypothesis at the time.
The main basic assumptions of the theory are:
- The particles of a gas (atoms, molecules) are of negligible size and are constantly in disordered but statistically detectable motion.
- Between their collisions they move uniformly and independently of each other, without preference for any direction.
- The particles do not exert forces on each other as long as they do not touch each other.
- Collisions of particles with each other and with the vessel wall obey the law of elastic impact. The collisions always involve only two particles.
From these assumptions, the kinetic theory of gases develops formulas that predict the quantities of pressure, specific heat, speed of sound, diffusion, heat conduction and internal friction for an ideal gas. The formulas reproduce well the observations made on many real gases and led, for example, to the first determinations of the size, number and mass of atoms or molecules. By supplementary additions to the assumptions nos. 3 and 4, the deviating behaviour of real gases was also included in the kinetic theory of gases, as described, for example, in the van der Waals equation of state.
See also
- Heat transfer
- Maxwell-Boltzmann distribution
- H-Theorem
Questions and Answers
Q: What is kinetic theory?
A: Kinetic theory is a scientific theory that explains the overall properties of gases, such as pressure, temperature, or volume, by considering their molecular composition and motion.
Q: What does kinetic theory state about pressure?
A: Kinetic theory states that pressure is not caused by molecules pushing each other away, like earlier scientists thought. Instead, pressure is caused by the molecules colliding with each other and their container.
Q: What is another name for kinetic theory?
A: Kinetic theory is also known as kinetic-molecular theory or collision theory.
Q: What are the three main components of kinetic theory?
A: The three main components of kinetic theory are the size and motion of gas molecules, the intermolecular forces between the molecules, and the amount of time for which these molecules interact with one another.
Q: What properties does kinetic theory attempt to explain?
A: Kinetic theory attempts to explain overall properties of gases, such as pressure, temperature, or volume.
Q: How does kinetic theory explain properties of gases?
A: Kinetic theory explains properties of gases by considering their molecular composition and motion.
Q: What earlier notion about pressure did kinetic theory refute?
A: Kinetic theory refuted the earlier notion that pressure is caused by molecules pushing each other away.
