Name: kinetic molecular theory and gas behavior
Uploaded: 2020-09-03T13:38:26.000Z
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PS.Chm.7.3

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Basic Postulates of Kinetic Molecular Theory: Particle Size, Energy, and Collision

Alors que les lois des gaz résument les relations entre les différentes propriétés des gaz idéaux, la théorie moléculaire cinétique explique pourquoi les gaz suivent les lois. La théorie est basée sur quelques hypothèses ou postulats. La première hypothèse est que les particules de gaz sont de taille négligeable.Un gaz est principalement un espace vide composé de petites particules qui sont séparées à des distances beaucoup plus grandes que leurs propres dimensions. Leur volume combiné est négligeable par rapport au volume total dans lequel le gaz est contenu. Contrairement aux solides et aux liquides, qui sont incompressibles en raison de leur espacement étroit entre les particules, les gaz sont fortement compressibles.Les particules de gaz sont dans un état de mouvement constant le long de lignes droites dans des directions aléatoires. Leurs chemins ne changent que lorsqu'ils entrent en collision avec d'autres particules ou avec les parois de leur conteneur. La deuxième hypothèse est que les particules de gaz ont des collisions parfaitement élastiques.Ils entrent en collision et rebondissent les uns des autres sans coller ensemble. Cela peut être comparé aux collisions entre les boules de billard pendant une partie de billard. Lorsque des particules de gaz entrent en collision, elles échangent de l'énergie les unes avec les autres, mais il n'y a pas de perte nette d'énergie.En d'autres termes, l'énergie totale du système reste constante. Les particules de gaz se déplacent constamment;par conséquent, elles possèdent de l'énergie cinétique. Ainsi, la troisième hypothèse indique que l'énergie cinétique moyenne d'un gaz est proportionnelle à sa température absolue en kelvin.Cela signifie que l'énergie cinétique augmente avec la température, et par conséquent, les particules se déplacent plus rapidement. À des températures plus élevées, leur vitesse augmente. Par contre, à mesure que la température diminue, l'énergie cinétique des particules diminue et elles se déplacent plus lentement.À une température donnée, tous les gaz, quelle que soit leur masse moléculaire, ont la même énergie cinétique moyenne. L'énergie cinétique est égale à la masse fois la vitesse au carré. Ainsi, pour que différents gaz aient la même énergie cinétique moyenne, leurs particules de gaz doivent voyager à des vitesses moyennes différentes.Par conséquent, les gaz plus lourds ont des vitesses moyennes plus faibles, tandis que les gaz plus légers ont des vitesses moyennes plus élevées. Par exemple, l'hélium et le néon, à la même température, ont la même énergie cinétique moyenne. Cependant, en raison de la différence de masse, les atomes de néon se déplacent beaucoup plus lentement que les atomes d'hélium.

théorie cinétique des gaz : postulats de base

L'équation du gaz parfait, qui est empirique, décrit le comportement des gaz en établissant des relations entre leurs propriétés macroscopiques. Par exemple, la loi de Charles stipule que le volume et la température sont directement liés. Par conséquent, les gaz se dilatent lorsqu'ils sont chauffés à pression constante. Bien que les lois sur les gaz expliquent comment les propriétés macroscopiques changent les unes par rapport aux autres, elles n'expliquent pas le raisonnement sur lequel elles sont fondées. 
 
 La théorie cinétique des gaz est un modèle microscopique qui permet de comprendre ce qui arrive aux particules de gaz au niveau moléculaire ou atomique, lorsque des conditions telles que la pression ou la température changent. En 1857, Rudolf Clausius a publié une forme complète et satisfaisante de la théorie, qui explique de manière efficace les différentes lois sur les gaz à partir des postulats qui ont été développés sur la base de centaines d'observations expérimentales sur le comportement des gaz. 
 
 Les principales caractéristiques de cette théorie sont les suivantes : 
 
 <ol>
 <li>Les gaz sont composés de particules (atomes ou molécules) en mouvement continu, se déplaçant en ligne droite et changeant de direction uniquement lorsqu'elles entrent en collision avec d'autres molécules ou avec les parois d'un récipient. 
 Examinez un échantillon du gaz argon à la température et à la pression standard. Il montre que seulement 0,01 % du volume est occupé par des atomes, avec une distance moyenne de 3,3 nm (le rayon atomique de l'argon est de 0,097 nm) entre deux atomes d'argon. La distance est beaucoup plus grande que ses propres dimensions. </li>
 <li>Les molécules composant le gaz ont une taille négligeable par rapport aux distances qui les séparent. Par conséquent, le volume combiné de toutes les particules de gaz est négligeable par rapport au volume total du récipient. Les particules sont considérées comme des “ points “ qui ont une masse mais un volume négligeable. </li>
 <li>La pression exercée par un gaz dans un récipient clos résulte de collisions entre les molécules de gaz et les parois du récipient. </li>
 <li>Les molécules de gaz n'exercent aucune force d'attraction ou de répulsion entre elles ou sur les parois du récipient ; par conséquent, leurs chocs sont élastiques (n'impliquent pas de perte d'énergie). 
 Lors de chocs élastiques, l'énergie est transférée entre les particules entrant en collision. L'énergie cinétique moyenne des particules demeure donc constante et ne change pas avec le temps. </li>
 <li>L'énergie cinétique moyenne des molécules de gaz est proportionnelle à la température en Kelvin du gaz. 
 Tous les gaz, quelle que soit leur masse moléculaire, ont la même énergie cinétique moyenne à la même température. </li>
 </ol>
 
 Ce texte est adapté de <a href="https://openstax.org/books/chemistry-2e/pages/9-5-the-kinetic-molecular-theory">Openstax, Chimie 2e, Chapitre 9.5 la théorie cinétique-moléculaire</a>.

Théorie cinétique des gaz : postulats de base

L’équation des gaz parfaits, qui est empirique, décrit le comportement des gaz en établissant des relations entre leurs propriétés macroscopiques. Pour...

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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.

Kinetic Molecular Theory and Gas Behavior

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definition and measurement of pressure: atmospheric pressure, barometer, and manometer

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Gas Pressure in Mixtures: Partial Pressures

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Stoichiometry of Gases with the Ideal Gas Law

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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...

kinetic molecular theory and gas laws explain properties of gas molecules

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Gas Pressure Patterns in Kinetic Molecular Theory

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Gas Particle Speed Distributions and Temperature

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key terms and concepts

Explore how kinetic molecular theory explains gas pressure, particle motion, elastic collisions, and why average kinetic energy depends on kelvin temperature.

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Kinetic Molecular Theory and Gas Behavior

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