Name: gas pressure patterns in kinetic molecular theory
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Kinetic Molecular Theory and Gas Laws Explain Properties of Gas Molecules

As observações das diferentes propriedades dos gases, conforme expresso pelas várias leis dos gases derivadas de Boyle, Charles, Gay-Lussac e Avogadro, seguem conceitualmente da teoria molcular cinética. A pressão exercida por um gás resulta do impacto das partículas em constante movimento nas pareces do seu recipiente. Diminuir o volume do recipiente, ao mesmo tempo que se mantém o número de mols e a temperatura constante, junta as partículas de gás, reduzindo o espaço entre si.Neste volume menor, a densidade do gás e a frequência de colisão a frequência de colisões molécula-parede aumenta. Desta forma, a pressão exercida pelo gás aumenta. A relação inversa entre a pressão e o volume é dada pela lei de Boyle.Adicionar mais mols de gás ao recipiente a uma temperatura constante aumenta a densidade do gás, e, desta forma, a frequência de colisão. Para manter a pressão inicial o volume tem de se expandir. Esta relação direta entre o volume e os mols é dada pela lei de Avogadro.Agora, consideremos que o número de mols é mantido constante e que a temperatura é aumentada. Porque a energia cinética média das partículas de gás aumenta proporcionalmente com a temperatura, as partículas colidem mais frequente e energicamente. Se o volume for mantido constante enquanto a temperatura for aumentada, a densidade do gás e a frequência de colisões aumenta, então aqui a pressão também aumentará.A relação direta entre a pressão e a temperatura é dada pela lei de Gay-Lussac. Se, por outro lado, a pressão se mantiver constante conjuntamente com um número constante de mols, então o aumento da temperatura tem de ser acompanhado pelo aumento do volume de forma a espalhar as colisões para uma área de superfície maior. Esta relação direta entre o volume e a temperatura é dada pela lei de Charles.Por fim, de acordo com a teoria molcular cinética, as partículas de gás não se atraem nem repelem umas às outras. Numa mistura de diferentes gases, os componentes atuam de forma independente e as suas pressões individuais mantêm-se inalteradas pela presença de outro gás. A pressão total da mistura é, por isso, a soma das pressões parciais individuais.Esta é a lei de Dalton.

teoria cinética molecular e as leis dos gases

O teste da teoria cinética molecular (KMT) e os seus postulados são a sua capacidade de explicar e descrever o comportamento de um gás. As várias leis de gases (leis de Boyle, Charles, Gay-Lussac, Avogadro, e Dalton) podem ser derivadas dos pressupostos da KMT, que levaram os químicos a acreditar que os pressupostos da teoria representam com precisão as propriedades das moléculas de gás.

<h4>A Teoria Cinética Molecular Explica o Comportamento dos Gases</h4>

Recordando que a pressão do gás é exercida por moléculas de gás que se movem rapidamente e depende diretamente do número de moléculas que atingem uma área unitária da parede por unidade de tempo, a KMT explica conceptualmente o comportamento de um gás da seguinte forma:

<ul>
<li>Lei de Gay-Lussac: Se a temperatura aumentar, a velocidade média e a energia cinética das moléculas de gás aumentam. Se o volume for mantido constante, o aumento da velocidade das moléculas de gás resulta em colisões mais frequentes e mais fortes com as paredes do recipiente, aumentando assim a pressão. Isto também é denominado de lei de Amontons.</li>
<li>Lei de Charles: Se a temperatura de um gás for aumentada, a pressão constante só poderá ser mantida se o volume ocupado pelo gás aumentar. Isto resultará em distâncias médias maiores percorridas pelas moléculas para alcançar as paredes do recipiente, bem como uma maior área da superfície da parede. Estas condições irão diminuir tanto a frequência de colisões de moléculas com a parede como o número de colisões por área de unidade, cujos efeitos combinados equilibram o efeito de forças de colisão aumentadas devido à maior energia cinética a uma temperatura mais elevada.</li>
<li>A lei de Boyle: Se o volume de gás for reduzido, a área da parede do recipiente diminui e a frequência de colisões de moléculas com a parede aumenta, ambos aumentando a pressão exercida pelo gás.</li>
<li>Lei de Avogadro: A uma pressão e temperatura constantes, a frequência e força das colisões das moléculas com a parede são constantes. Nessas condições, aumentar o número de moléculas gasosas exigirá um aumento proporcional do volume do recipiente, de modo a produzir uma diminuição no número de colisões por área de unidade para compensar o aumento da frequência de colisões. </li>
<li>A lei de Dalton: Devido às grandes distâncias entre elas, as moléculas de um gás em uma mistura bombardeiam as paredes do recipiente com a mesma frequência, quer estejam presentes outros gases ou não, e a pressão total de uma mistura de gases equivale à soma das pressões (parciais) dos gases individuais.</li>
</ul>

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

Teoria Cinética Molecular e as Leis dos Gases

O teste da teoria cinética molecular (KMT) e seus postulados é sua capacidade de explicar e descrever o comportamento de um gás. As várias leis do gás ...

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gas pressure patterns in kinetic molecular theory

Kinetic molecular theory explains gas pressure by linking it to the motion of gas molecules. Gas pressure comes from rapidly moving molecules hitting the walls of a container. It depends on how many molecules strike a unit area in a given time.

The theory also helps explain the main gas laws. In Gay-Lussac’s law, also called Amontons’s law, raising temperature increases the average speed and kinetic energy of gas molecules. If volume stays constant, the molecules collide with the walls more often and more forcefully, so pressure increases.

Charles’s law shows what happens when temperature rises at constant pressure. The gas must expand to keep pressure steady. That larger volume means molecules travel farther before reaching the walls, and the wall area increases too. These changes lower collision frequency and the number of collisions per unit area, which balances the stronger collisions caused by the higher kinetic energy.

Boyle’s law describes the effect of smaller volume. When gas volume decreases, the container wall area also decreases. Molecule-wall collisions become more frequent, and the pressure rises. Avogadro’s law says that at constant pressure and temperature, the collision rate and collision force stay constant. If the number of gas molecules increases, the volume must increase in proportion so the collisions per unit area can drop enough to offset the added molecules.

Dalton’s law applies to gas mixtures. Because gas molecules are far apart, one gas in a mixture strikes the container walls with the same frequency whether other gases are present or not. The total pressure of the mixture equals the sum of the partial pressures of the individual gases. These gas laws show how the assumptions of kinetic molecular theory fit the behavior of gases.

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kinetic molecular theory and gas laws explain properties of gas molecules

Kinetic molecular theory explains gas pressure by linking it to the motion of gas molecules. Gas pressure comes from rapidly moving molecules hitting the walls of a container. It depends on how many molecules strike a unit area in a given time. The theory also helps explain the main gas laws. In Gay-Lussac’s law, also called Amontons’s law, raising temperature increases the average speed and kinetic energy of gas molecules. If volume stays constant, the molecules collide with the walls more...

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Explore how kinetic molecular theory explains gas pressure, temperature, volume changes, and the gas laws of Boyle, Charles, Gay-Lussac, Avogadro, and Dalton.

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Gas Pressure Patterns in Kinetic Molecular Theory

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