Models of Gas Behaviour

Models of Gas Behaviour

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The models of gas behaviour are used to explain how gases interact with matter and their physical properties. There are many different models, such as the Democritus model, Bernoulli's model, and the kinetic model. The Democritus model was first postulated about 2400 years ago and believed that objects are made up of tiny uniform pieces, called atomos. Robert Boyle discovered that under controlled conditions, the pressure of a gas is inversely proportional to the volume of the gas. Guillaume Amontons and Joseph Lussac discovered a relation between temperature and pressure of the gas when the volume is constant. Jacques Charles found that gases expand in volume when heated. John Dalton discovered that the pressure of a mixture of gases is the sum of the pressures of the individual gases in the mixture. Amedeo Avogadro proposed that gases consist of very small particles, which he called molecules, and that equal volumes of gases under the same conditions of temperature and pressure contain equal numbers of molecules.

Ideal gas equation

Émile Clapeyron combined the laws of Boyle, Charles, and Avogadro to create the ideal gas equation. This equation states that the product of pressure and volume of a gas is equal to the product of the temperature, the amount of substance in molecules, and the gas constant. The gas constant has a value of 0.0821 atm⋅L/mol⋅K and is a measure of the energy per mole. The ideal gas equation is expressed as PV = nRT, where P is pressure in atm, V is volume in litres, n is the number of moles, R is the gas constant, and T is the temperature in Kelvin. (Visit Ideal Gas Law for more information)

Daniel Bernoulli model

Bernoulli was a scientist who studied the behaviour of liquid through a pipe with varying diameters. He believed that gases and all matter consisted of tiny particles, which helped develop the modern kinetic theory. Bernoulli's principle states that for ideal fluids, such as liquids and gases, pressure and velocity are inversely proportional. His theory is also expressed in terms of energy, where energy per unit volume is conserved. Bernoulli's principle is one of the most important guides used in aircraft for wing construction. The wing has a specific shape, which results in less pressure on the top of the wing compared to the bottom due to its curved top surface. This creates a force pushing the wing upwards, as the high-pressure particles move upwards to the less-pressured area.

Bernoulli's principle applied to an aircraft wing
Bernoulli's principle applied to an aircraft wing

According to the kinetic theory, matter is made up of small particles that are in constant motion. These particles possess energy, which is the driving force behind their continuous movement. The amount of energy that these particles possess depends on the temperature of the surrounding matter. Based on their energy levels, matter can exist in three states: solid, gas, and liquid. Despite its validity, the kinetic theory was not widely accepted when it was first proposed.


File:States-of-matter-template.svg - Wikimedia Commons
States of matter

Brownian motion

Brown, an English botanist, noticed that pollen seeds immersed in water move randomly in irregular circular motions. This led him to discover that any physical quantity submerged in a fluid experiences random fluctuations. The phenomenon was later explained as the result of small collisions between the submerged particles and other moving particles of the fluid, and was named Brownian motion. This theory further supports the kinetic theory, as Brownian motion provides evidence that air is made up of tiny atoms or molecules moving randomly in a medium.

Kinetic theory of gas

Rudolf Clausius revised Bernoulli's kinetic theory by introducing the concept of the mean free path of each individual particle and relating temperature to the gas-particle speed. James Maxwell continued Clausius' work by proposing the Maxwell distribution, the first statistical law in physics that predicts the range of speeds of particles in ideal gases. The kinetic theory of gas assumes that the molecules are small relative to the distance between them and are in constant random motion, causing multiple collisions. The molecules have physical properties such as mass, momentum, and energy. The temperature of the gas is a measure of the kinetic energy of the gas molecules, which increases their random motion depending on the temperature. The kinetic theory of gas is currently the most accepted theory for gas behavior, building on earlier models such as Democ' model.

Models of Gas Behaviour

What are four different models of gas?

Four different models of gases include the Democritus model, Kinetic model, Brown model and Bernoulli's model.

What is the most valid model of gases?

The most valid model of gases is the kinetic theory.

What is a gas model?

A gas model explains the behaviour and structure of gases.

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