Name: kinetic molecular theory and gas behavior
Uploaded: 2020-09-03T13:38:26.000Z
Duration: 2 min 43 s
Channel: JoVE

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NC K-12 Science Standard Course of Study

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Energy

PS.Chm.7.3

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

Podczas gdy prawa gazowe podsumowują relacje między różnymi właściwościami gazów doskonałych, kinetyczna teoria molekularna wyjaśnia, dlaczego gazy podlegają tym prawom. Teoria opiera się na kilku założeniach lub postulatach.

Pierwszym założeniem jest to, że cząstki gazu mają znikome rozmiary. Gaz to w większości pusta przestrzeń składająca się z małych cząstek, które są oddzielone od siebie na odległości znacznie większe niż ich własne wymiary. Ich łączna objętość jest znikoma w stosunku do całkowitej objętości, w której zawarty jest gaz.

W przeciwieństwie do ciał stałych i cieczy, które są nieściśliwe ze względu na bliskie odstępy między cząstkami, gazy są wysoce ściśliwe.

Cząsteczki gazu są w ciągłym ruchu wzdłuż linii prostych w losowych kierunkach. Ich ścieżki zmieniają się tylko wtedy, gdy zderzają się z innymi cząstkami lub ze ściankami swojego pojemnika. 

Drugim założeniem jest to, że cząstki gazu mają doskonale sprężyste zderzenia. Zderzają się i odbijają od siebie, nie sklejając się ze sobą. Można to porównać do zderzeń kul bilardowych podczas gry w bilard.

Kiedy cząsteczki gazu zderzają się, wymieniają ze sobą energię, ale nie ma straty netto energii. Innymi słowy, całkowita energia systemu pozostaje stała. 

Cząsteczki gazu są w ciągłym ruchu, dlatego posiadają energię kinetyczną. Tak więc trzecie założenie mówi, że średnia energia kinetyczna gazu jest proporcjonalna do jego temperatury bezwzględnej w kelwinach. 

Oznacza to, że energia kinetyczna wzrasta wraz z temperaturą, a co za tym idzie, cząstki poruszają się szybciej. W wyższych temperaturach ich prędkość wzrasta.

I odwrotnie, wraz ze spadkiem temperatury spada energia kinetyczna cząstek, które poruszają się wolniej.

W danej temperaturze wszystkie gazy, niezależnie od ich masy cząsteczkowej, mają tę samą średnią energię kinetyczną. Energia kinetyczna jest równa 1/2 masy razy prędkość podniesiona do kwadratu. Tak więc, aby różne gazy miały tę samą średnią energię kinetyczną, ich cząstki gazu muszą poruszać się z różnymi średnimi prędkościami. Dlatego cięższe gazy mają niższe prędkości średnie, podczas gdy lżejsze gazy mają wyższe prędkości średnie. 

Na przykład hel i neon, gdy są w tej samej temperaturze, mają tę samą średnią energię kinetyczną. Jednak ze względu na różnicę w ich masach, atomy neonu poruszają się znacznie wolniej niż atomy helu.

podstawowe postulaty teorii kinetyki molekularnej: wielkość cząstek, energia i zderzenie

Równanie gazu doskonałego, które ma charakter empiryczny, opisuje zachowanie gazów poprzez ustalenie zależności między ich właściwościami makroskopowymi. Na przykład prawo Charlesa stwierdza, że objętość i temperatura są ze sobą bezpośrednio powiązane, dlatego gazy rozszerzają się po podgrzaniu pod stałym ciśnieniem. Chociaż prawa gazowe wyjaśniają, w jaki sposób właściwości makroskopowe zmieniają się względem siebie, nie wyjaśniają powodów, które za tym stoją.

Kinetyczna teoria molekularna to model mikroskopowy, który pomaga zrozumieć, co dzieje się z cząsteczkami gazu na poziomie molekularnym lub atomowym, gdy zmienia się ich ciśnienie lub temperatura. W 1857 roku Rudolf Clausius opublikował kompletną i satysfakcjonującą teorię, która skutecznie wyjaśnia różne prawa gazowe poprzez postulaty opracowane na podstawie setek eksperymentalnych obserwacji zachowania gazów.

Zasadnicze cechy tej teorii to:

<ol style="display: flex; flex-direction: column; gap: 10px;">
 <li>Gazy składają się z cząstek (atomów lub cząsteczek), które są w ciągłym ruchu, poruszają się po liniach prostych i zmieniają kierunek tylko wtedy, gdy zderzają się z innymi cząsteczkami lub ze ściankami pojemnika.</li>
 <li>Zbadaj próbkę argonu w standardowej temperaturze i ciśnieniu. Wynika z niego, że tylko 0,01% objętości zajmują atomy znajdujące się w średniej odległości 3,3 nm (promień atomowy argonu wynosi 0,097 nm) pomiędzy dwoma atomami argonu. Odległość jest znacznie większa niż wymiar cząsteczki.</li>
 <li>Cząsteczki tworzące gaz są znikomo małe w porównaniu z odległościami między nimi. Dlatego łączna objętość wszystkich cząstek gazu jest pomijalna w stosunku do całkowitej objętości pojemnika. Cząstki uważa się za „punkty”, które mają masę, ale znikomą objętość.</li>
 <li>Ciśnienie wywierane przez gaz w pojemniku wynika z zderzeń cząsteczek gazu ze ściankami pojemnika.</li>
 <li>Cząsteczki gazu nie wywierają sił przyciągających ani odpychających na siebie nawzajem ani na ścianki pojemnika; dlatego ich zderzenia są sprężyste (nie powodują utraty energii).</li>
 <li>Podczas zderzeń sprężystych energia przekazywana jest pomiędzy zderzającymi się cząstkami. Zatem średnia energia kinetyczna cząstek pozostaje stała i nie zmienia się w czasie.</li>
 <li>Średnia energia kinetyczna cząsteczek gazu jest proporcjonalna do temperatury gazu w stopniach Kelvina.</li>
</ol>

Wszystkie gazy, niezależnie od masy cząsteczkowej, mają tę samą średnią energię kinetyczną w tej samej temperaturze.

Podstawowe postulaty teorii kinetyki molekularnej: wielkość cząstek, energia i zderzenie

Równanie gazu idealnego, które jest empiryczne, opisuje zachowanie gazów poprzez ustalenie zależności między ich właściwościami makroskopowymi. Dla...

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Chemia

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Gazy

KEY TERMS AND CONCEPTS

Kluczowe terminy i pojęcia

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

kinetic-molecular-theory-and-gas-behavior

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

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Pressure Units and Tools for Gas Measurement

Pressure is the force applied to a given area, and gas pressure comes from gas molecules colliding with surfaces. Each collision is tiny, but many collisions over a small area can create high pressure. Pressure increases when force increases or when the area gets smaller. It decreases when force drops or when the area gets larger. Pressure is measured in pascals, or Pa, in the SI system. One pascal equals 1 newton per square meter, and a newton is a unit of force equal to 1 kg·m/s2. A pascal...

gas laws: boyle's, gay-lussac, charles', avogadro's, and ideal gas law

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How Gas Pressure, Volume, and Temperature Change

Gas pressure, volume, temperature, and amount are linked by several gas laws. Scientists found these relationships by studying how a confined gas changes when one variable is held constant and another changes. These patterns apply to an ideal gas, which is a useful model for gases under low pressure and high temperature. Gay-Lussac’s law, also called Amontons’s law, connects pressure and temperature. If gas is trapped in a rigid container, the volume and number of moles stay constant. When the...

applications of the ideal gas law: molar mass, density, and volume

applications-of-the-ideal-gas-law-molar-mass-density-and-volume

Ideal Gas Law at STP and Gas Density

The ideal gas law links pressure, volume, number of moles, and temperature. It helps explain how gas volume changes when pressure or temperature changes. At standard temperature and pressure, or STP, the values are 273.15 K and 1 atm. At STP, one mole of an ideal gas occupies about 22.4 L. This is called the standard molar volume. The gas can be hydrogen, oxygen, argon, or carbon dioxide, and the volume is still about 22.4 liters. Half a mole occupies 11.2 L, and 2 moles occupy 44.8 L. The...

mixtures of gases: dalton's law of partial pressures and mole fractions

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Gas Pressure in Mixtures: Partial Pressures

Gas pressure in mixtures is described by partial pressure and mole fraction. When gases do not chemically react, each gas in the mixture acts as if it were alone in the container. The pressure from one gas is called its partial pressure. For a mixture of three gases, A, B, and C, the total pressure equals the sum of their partial pressures: PA, PB, and PC. This is Dalton's law of partial pressures. It states that the total pressure of a mixture of ideal gases is the sum of the pressures from...

chemical stoichiometry and gases: using ideal gas law to determine moles

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Stoichiometry of Gases with the Ideal Gas Law

Chemical stoichiometry links the amounts of reactants and products in a chemical reaction. For gases, those amounts can also be measured by volume. If a gas’s volume, pressure, and temperature are known, the ideal gas equation can be used to find the number of moles present. The same idea works in reverse. If the moles of a gas are known, its volume can be found at any temperature and pressure. The transcript gives an example using 8.88 g of gallium reacting with excess hydrochloric acid.

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

kinetic-molecular-theory-gas-laws-explain-properties-gas

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...

kinetic molecular theory: molecular velocities, temperature, and kinetic energy

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Gas Particle Speed Distributions and Temperature

Gas particle speed distributions and temperature are key ideas in the kinetic molecular theory. This theory explains the gas laws by describing how gas molecules move, collide, and share energy. Gas molecules do not all move at the same speed. A gas sample has an average speed and an average kinetic energy, but individual molecules move at different speeds. Their collisions are elastic, which means momentum is conserved. Because so many molecules collide, the overall speed distribution stays...

behavior of gas molecules: molecular diffusion, mean free path, and effusion

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Gas Particle Motion, Diffusion, and Effusion

Gas particle motion, diffusion, and effusion explain how gases spread and escape in everyday settings. Gas molecules move at very high speeds, but they collide with other gas molecules and change direction many times before reaching a target. At room temperature, a gas molecule can experience billions of collisions each second. The mean free path is the average distance a molecule travels between collisions. This distance becomes larger when pressure decreases. In general, the mean free path...

real gases: effects of intermolecular forces and molecular volume deriving van der waals equation

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Real Gases: When the Ideal Gas Law Breaks Down

Real gases are gases that do not always follow the ideal gas law, PV = nRT, especially when pressure is high or temperature is low. The ideal gas model assumes gas particles have no attractive or repulsive forces and take up negligible space compared with the container. At room temperature and 1 atm or less, many gases behave close to ideally. When conditions change, the measured relationships between pressure, volume, and temperature can drift away from the ideal prediction. One way to see...

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.

Kinetic Molecular Theory and Gas Behavior | JoVE K12

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New York State Science Learning Standards

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Classifying Matter by State

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Classifying Matter by Composition

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Physical Properties of Matter

A physical property is ...

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Intermolecular vs Intramolecular Forces

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Surface Tension
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States of Matter and Phase Changes

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Phase Transitions

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Phase Transitions: Vaporization and Condensation

The physical form of a substance changes on changing its temperature. For example, raising the temperature of a liquid causes the liquid to vaporize ...

Vapor Pressure

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Clausius-Clapeyron Equation

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Phase Transitions: Melting and Freezing

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Phase Transitions: Sublimation and Deposition

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Heating and Cooling Curves

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Phase Diagrams

A phase diagram combines plots of pressure versus temperature for the liquid-gas, solid-liquid, and solid-gas phase-transition equilibria of a substance. ...

Use models to explain how changes in energy affect the arrangement and movement of the particles in solids, liquids, and gases, as well as the relative strengths of their intermolecular forces.

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Energy Basics

Chemical reactions, such as those that occur when you light a match, involve changes in energy as well as matter.

Chemical changes and their accompanying ...

First Law of Thermodynamics

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Energy can be converted from one form into another, but all of the energy present before a change occurs always exists in some form ...

Internal Energy

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Quantifying Heat

Thermal Energy&#160;

Microscopically, thermal energy is the kinetic energy associated with the random motion of atoms and molecules. Temperature is a ...

Quantifying Work

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Enthalpy

Chemists ordinarily use a property known as enthalpy (H) to describe the thermodynamics of chemical and physical processes. Enthalpy is defined as the sum ...

Thermochemical Equations

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Constant Pressure Calorimetry

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Constant Volume Calorimetry

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Source: Laboratory of Dr. Terry Tritt &#8212; Clemson University
Differential Scanning Calorimetry (DSC) is a method of thermodynamic analysis based on ...

Hess's Law

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Standard Enthalpy of Formation

Enthalpy changes are typically tabulated for reactions in which both the reactants and products are at the same conditions. A standard state is a commonly ...

Enthalpies of Reaction

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Use mathematics and computational thinking to execute simple calorimetric calculations based on the Law of Conservation of Energy.

PS.Chm.7.2

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Applications of the Ideal Gas Law: Molar Mass, Density, and Volume

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Mixtures of Gases: Dalton's Law of Partial Pressures and Mole Fractions

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Chemical Stoichiometry and Gases: Using Ideal Gas Law to Determine Moles

Chemical stoichiometry describes the quantitative relationships between reactants and products in chemical reactions.

In addition to measuring quantities ...

The ideal-gas equation, which is empirical, describes the behavior of gases by establishing relationships between their macroscopic properties. For ...

Kinetic Molecular Theory and Gas Laws Explain Properties of Gas Molecules

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Kinetic Molecular Theory: Molecular Velocities, Temperature, and Kinetic Energy

The kinetic molecular theory qualitatively explains the behaviors described by the various gas laws. The postulates of this theory may be applied in a ...

Behavior of Gas Molecules: Molecular Diffusion, Mean Free Path, and Effusion

Although gaseous molecules travel at tremendous speeds (hundreds of meters per second), they collide with other gaseous molecules and travel in many ...

Real Gases: Effects of Intermolecular Forces and Molecular Volume Deriving Van der Waals Equation

Thus far, the ideal gas law, PV = nRT, has been applied to a variety of different types of problems, ranging from reaction stoichiometry and empirical and ...

Ideal Gas Law

Source: Laboratory of Dr. Andreas Z&#252;ttel - Swiss Federal Laboratories for Materials Science and Technology
The ideal gas law describes the behavior ...

Derivation of the Ideal Gas Law
Gases are a fundamental state of matter. A gas is a collection of molecules that have a significant distance between their ...

Source: Smaa Koraym at Johns Hopkins University, MD, USA

	Preparation of the LaboratoryExpand
	Here, we show the laboratory preparation for 10 students ...

Source: Smaa Koraym at Johns Hopkins University, MD, USA

	Determining the Mass of the Unknown LiquidExpand
	According to the ideal gas law for a given ...

Use mathematics and computational thinking to explain the relationships among pressure, temperature, volume, and quantity of gas, both qualitatively and quantitatively.

Understand the relationship among pressure, temperature, volume, and phase.

Kinetic Molecular Theory and Gas Behavior

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