Name: kinetic molecular theory and gas behavior
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Basic Postulates of Kinetic Molecular Theory: Particle Size, Energy, and Collision

Enquanto que as leis do gás resumem as relações entre as diferentes propriedades dos gases ideais, a teoria molecular cinética explica porque os gases seguem as leis. A teoria baseia-se em alguns pressupostos ou postulados. O primeiro pressuposto é que as partículas de gás são insignificantes em termos de tamanho.Um gás é maioritariamente um espaço vazio composto por pequenas partículas que estão separadas a distâncias maiores do que as suas próprias dimensões. O seu volume combinado é insignificante em relação ao volume total em que o gás está contido. Contrariamente aos sólidos e líquidos, que são incompressíveis devido ao estreito espaçamento entre as partículas, os gases são altamente compressíveis.As partículas de gás estão em constante movimento ao longo de linhas retas em direções aleatórias. Os seus percursos só se alteram quando elas colidem com outras partículas ou com as paredes do seu recipiente. O segundo pressuposto é que as partículas de gás têm colisões perfeitamente elásticas.Elas colidem e afastam-se umas das outras sem ficarem unidas. Isto pode ser comparado às colisões existentes entre as bolas de bilhar durante um jogo de bilhar. Quando as partículas de gás colidem, elas trocam energia entre si, mas não há nenhuma perda líquida de energia.Por outras palavras, a energia total do sistema permanece constante. As partículas de gás estão em constante movimento;por isso, têm energia cinética. Assim, o terceiro pressuposto afirma que a energia cinética média de um gás é proporcional à sua temperatura absoluta em kelvin.Isto significa que a energia cinética aumenta com a temperatura, e como consequência, as partículas movem-se mais rapidamente. A temperaturas mais elevadas, a sua velocidade aumenta. Por outro lado, à medida que a temperatura diminui, também diminui a energia cinética das partículas, e elas movem-se mais lentamente.A uma certa temperatura, todos os gases, independentemente da sua massa molecular, têm a mesma energia cinética média. A energia cinética é igual à massa vezes a velocidade ao quadrado. Assim, para que diferentes gases tenham a mesma energia cinética média, as suas partículas de gás têm de se movimentar a diferentes velocidades médias.Desta forma, os gases mais pesados têm velocidades médias mais baixas, enquanto que os gases mais leves têm velocidades médias mais elevadas. Por exemplo, o hélio e o néon, quando estão à mesma temperatura, têm a mesma energia cinética média. Contudo, devido à diferenças das suas massas, os átomos de néon movem-se mais lentamente do que os átomos de hélio.

teoria cinética molecular: postulados básicos

A equação de gás ideal, que é empírica, descreve o comportamento dos gases estabelecendo relações entre as suas propriedades macroscópicas. Por exemplo, a lei de Charles afirma que o volume e a temperatura estão diretamente relacionados. Por conseguinte, os gases expandem quando aquecidos a uma pressão constante. Embora as leis do gases expliquem como as propriedades macroscópicas se alteram em relação umas às outras, não explicam a lógica por trás delas.

A teoria cinética molecular é um modelo microscópico que ajuda a perceber o que acontece com partículas de gases a nível molecular ou atómico quando condições como pressão ou temperatura mudam. Em 1857, Rudolf Clausius publicou uma forma completa e satisfatória da teoria, que explica efetivamente as diferentes leis de gases através de postulados que foram desenvolvidos com base em centenas de observações experimentais do comportamento dos gases.

As características salientes desta teoria são:

<ol>
<li>Os gases são compostos por partículas (átomos ou moléculas) que estão em movimento contínuo, viajando em linhas retas e mudando de direção apenas quando colidem com outras moléculas ou com as paredes de um recipiente. 
Ao examinar uma amostra de gás árgon à temperatura e pressão padrão, ela mostra que apenas 0,01% do volume é ocupado por átomos com uma distância média de 3,3 nm (o raio atómico do árgon é de 0,097 nm) entre dois átomos de árgon. A distância é muito maior do que a sua própria dimensão.</li>
<li>As moléculas que compõem o gás são negligentemente pequenas em comparação com as distâncias entre elas. Por conseguinte, o volume combinado de todas as partículas de gás é insignificante em relação ao volume total do recipiente. As partículas são consideradas “pontos” que têm massa , mas volume insignificante.</li>
<li>A pressão exercida por um gás em um recipiente resulta de colisões entre as moléculas de gás e as paredes do recipiente.</li>
<li>As moléculas de gás não exercem forças de atração ou repulsão umas sobre as outras ou nas paredes do recipiente; portanto, as suas colisões são elásticas (não envolvem perda de energia). 
Durante colisões elásticas, a energia é transferida entre as partículas em colisão. A energia cinética média das partículas, portanto, permanece constante e não muda com o tempo.</li>
<li>A energia cinética média das moléculas de gás é proporcional à temperatura em kelvin do gás. 
Todos os gases, independentemente da sua massa molecular, têm a mesma energia cinética média à mesma temperatura.</li>
</ol>

Este texto é adaptado de <a href="https://openstax.org/books/chemistry-2e/pages/9-5-the-kinetic-molecular-theory">Openstax, Chemistry 2e, Chapter 9.5 The Kinetic-Molecular Theory</a>.

Teoria Cinética Molecular: Postulados Básicos

A equação do gás ideal, que é empírica, descreve o comportamento dos gases estabelecendo relações entre suas propriedades macroscópicas. Durante...

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kinetic molecular theory and gas behavior

Kinetic molecular theory explains gas behavior at the particle level. It gives a microscopic model for what happens when pressure or temperature changes. Gas laws describe how macroscopic properties change, but they do not explain why those changes happen.

The theory was put into a complete form by Rudolf Clausius in 1857. It was built from hundreds of experimental observations about gases. Those observations helped explain the different gas laws through a few basic postulates.

One key idea is that gases are made of particles, either atoms or molecules, that move constantly. They travel in straight lines until they collide with other particles or with the walls of a container. A sample of argon gas at standard temperature and pressure shows that the particles take up only a tiny part of the total volume. The average distance between two argon atoms is much larger than the size of the atoms themselves. Because of this, gas particles are treated as points with mass but negligible volume.

Gas pressure comes from collisions between gas molecules and the walls of the container. The particles do not attract or repel each other, and they do not interact with the container walls through such forces. For that reason, their collisions are elastic, which means no energy is lost in the collision. Energy can still be transferred between colliding particles, but the average kinetic energy stays constant over time.

The average kinetic energy of gas particles depends on the kelvin temperature of the gas. It is proportional to temperature. At the same temperature, gases with different molecular masses have the same average kinetic energy.

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basic postulates of kinetic molecular theory: particle size, energy, and collision

Kinetic molecular theory explains gas behavior at the particle level. It gives a microscopic model for what happens when pressure or temperature changes. Gas laws describe how macroscopic properties change, but they do not explain why those changes happen. The theory was put into a complete form by Rudolf Clausius in 1857. It was built from hundreds of experimental observations about gases. Those observations helped explain the different gas laws through a few basic postulates. One key idea...

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Kinetic Molecular Theory and Gas Behavior

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