Name: kinetic molecular theory and gas behavior
Uploaded: 2020-09-03T13:38:26.000Z
Duration: 2 min 43 s
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Basic Postulates of Kinetic Molecular Theory: Particle Size, Energy, and Collision

Mentre le leggi dei gas riassumono le relazioni fra le diverse proprietà dei gas ideali, la teoria molecolare cinetica spiega perché i gas seguono queste leggi. La teoria si basa su alcuni presupposti o postulati. La prima ipotesi è che le particelle di gas siano di dimensioni trascurabili.

Un gas è per lo più uno spazio vuoto composto da piccole particelle che sono separate a distanze ben maggiori delle loro stesse dimensioni. Il loro volume combinato è trascurabile rispetto al volume totale in cui è contenuto il gas. Contrariamente ai solidi e ai liquidi, che sono incomprimibili a causa della loro stretta distanza tra le particelle, i gas sono altamente comprimibili.

Le particelle di gas sono in uno stato di movimento costante lungo linee rette in direzioni casuali. I loro percorsi cambiano solo quando entrano in collisione con altre particelle o con le pareti del loro contenitore. La seconda ipotesi è che le particelle di gas abbiano collisioni perfettamente elastiche.

Queste si scontrano e rimbalzano l'una dall'altra senza attaccarsi. Questo può essere paragonato alla collisione tra le palle da biliardo durante una partita. Quando le particelle di gas entrano in collisione, scambiano energia fra loro, ma non vi è alcuna perdita netta di energia.

In altre parole, l'energia totale del sistema rimane costante. Le particelle di gas sono in continuo movimento;quindi, possiedono energia cinetica. Pertanto, la terza ipotesi afferma che l'energia cinetica media di un gas è proporzionale alla sua temperatura assoluta in Kelvin.

Questo significa che l'energia cinetica aumenta con la temperatura e, di conseguenza, le particelle si muovono più velocemente. A temperature più elevate, la loro velocità aumenta. Al contrario, al diminuire della temperatura, diminuisce anche l'energia cinetica delle particelle, che si muovono più lentamente.

A una data temperatura, tutti i gas, a prescindere dalla loro massa molecolare, hanno la stessa energia cinetica media. L'energia cinetica è uguale alla massa moltiplicata per la velocità al quadrato. Pertanto, affinché gas diversi abbiano la stessa energia cinetica media, le loro particelle di gas devono viaggiare a velocità medie diverse.

Pertanto, i gas più pesanti hanno velocità medie inferiori, mentre i gas più leggeri hanno velocità medie più elevate. Per esempio, l'elio e il neon, alla stessa temperatura, hanno la stessa energia cinetica media. Tuttavia, a causa della differenza nelle loro masse, gli atomi di neon si muovono molto più lentamente degli atomi di elio.

postulati di base della teoria molecolare cinetica: dimensione delle particelle, energia e collisione

L'equazione dei gas ideali, che empirica, descrive il comportamento dei gas stabilendo relazioni tra le loro propriet macroscopiche. Ad esempio, la legge di Charles afferma che il volume e la temperatura sono direttamente correlati. I gas, quindi, si espandono quando riscaldati a pressione costante. Sebbene le leggi dei gas spieghino come le propriet macroscopiche cambiano l’una rispetto all’altra, non ne spiegano la logica.

La teoria cinetica molecolare un modello microscopico che aiuta a capire cosa succede alle particelle di gas a livello molecolare o atomico quando cambiano le condizioni come la pressione o la temperatura. Nel 1857 Rudolf Clausius pubblic una forma completa e soddisfacente della teoria, che spiega efficacemente le diverse leggi dei gas attraverso i postulati sviluppati sulla base di centinaia di osservazioni sperimentali del comportamento dei gas.

Le caratteristiche salienti di questa teoria sono:

<ol>
	<li>I gas sono composti da particelle (atomi o molecole) che sono in continuo movimento, viaggiando in linea retta e cambiando direzione solo quando entrano in collisione con altre molecole o con le pareti di un contenitore.</li>
	<li>Esaminare un campione di gas argon a temperatura e pressione standard, mostra che solo lo 0,01% del volume occupato da atomi con una distanza media di 3,3 nm (il raggio atomico dell'argon 0,097 nm) tra due atomi di argon. La distanza molto maggiore della sua stessa dimensione.</li>
	<li>Le molecole che compongono il gas sono trascurabilmente piccole rispetto alla distanza che le separa. Pertanto, il volume combinato di tutte le particelle di gas trascurabile rispetto al volume totale del contenitore. Le particelle sono considerate “punti? che hanno una massa e volume trascurabile.</li>
	<li>La pressione esercitata da un gas in un contenitore risulta dalle collisioni tra le molecole del gas e le pareti del contenitore.</li>
	<li>Le molecole di gas non esercitano forze attrattive o repulsive tra loro o sulle pareti del contenitore; pertanto i loro urti sono elastici (non comportano una perdita di energia).</li>
	<li>Durante gli urti elastici, l'energia viene trasferita tra le particelle in collisione. L'energia cinetica media delle particelle, quindi, rimane costante e non cambia nel tempo.</li>
	<li>L'energia cinetica media delle molecole di gas proporzionale alla temperatura Kelvin del gas.</li>
	<li>Tutti i gas, indipendentemente dalla loro massa molecolare, hanno la stessa energia cinetica media alla stessa temperatura.</li>
</ol>

Questo testo adattato da <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>

Postulati di base della teoria molecolare cinetica: dimensione delle particelle, energia e collisione

L'equazione dei gas ideali, che è empirica, descrive il comportamento dei gas stabilendo relazioni tra le loro proprietà macroscopiche. Per...

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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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