Name: gas pressure in mixtures: partial pressures
Uploaded: 2020-09-03T13:38:26.000Z
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Mixtures of Gases: Dalton's Law of Partial Pressures and Mole Fractions

De druk van een zuiver gas is de som van moleculaire botsingen tussen de deeltjes en de omliggende oppervlakken. Een gasmonster met minder deeltjes in een bepaald volume oefent een lagere druk uit dan een monster met meer deeltjes in hetzelfde volume. Maar wat is de druk van een mengsel van verschillende gassen?Voor een gasmengsel dat uit meerdere componenten bestaat, is de druk de som van botsingen van alle gasmoleculen. Aangenomen wordt dat elke component in het mengsel zijn eigen druk uitoefent die onafhankelijk is van de andere aanwezige gassen. De druk van een afzonderlijk onderdeel wordt de partiële druk genoemd.De totale druk van het ideale gasmengsel is gelijk aan de som van de partiële drukken van de componenten. Deze waarneming is de wet van Dalton van partiële druk. Door de ideale gaswet toe te passen, worden de partiële drukken van de afzonderlijke gascomponenten vervangen door meetbare variabelen.Omdat de gassen in het mengsel hetzelfde volume innemen en dezelfde temperatuur hebben, kan de vergelijking worden vereenvoudigd. De som van de molen van de afzonderlijke componenten is gelijk aan het totale aantal molen van alle gascomponenten, n-totaal. Daarom is de totale druk van het gasmengsel gelijk aan het n-totaal vermenigvuldigd met de constante R-T gedeeld door V.Het aantal molen van een component gedeeld door het totaal aantal molen in het mengsel is de molfractie.Het herschikken van de molfractie voor het totale aantal molen en het vervangen van n-totaal in de wet van Dalton van partiële drukken levert uitdrukkingen op voor de totale druk. Als je opnieuw herschikt, is de partiële druk van een gas in een mengsel het product van zijn molfractie en de totale druk van het mengsel. Dus in een gasmengsel is de partiële druk van een component, i, gelijk aan de molfractie van i vermenigvuldigd met de totale druk.Stel als voorbeeldberekening dat een container gevuld met twee gassen, helium en argon, 40 vol. argon is. Dit impliceert dat de molfractie van argon 0, 4 is.Als de totale druk 4 atmosfeer is, wat is dan de partiële druk van helium? Met behulp van de vergelijking voor de partiële druk van een gas, is de partiële druk van argon gelijk aan de molfractie vermenigvuldigd met de totale druk. Dus 0, 4 keer 4 atmosfeer geeft de partiële druk van argon als 1, 6 atmosfeer.Aangezien de som van de partiële drukken gelijk is aan de totale druk, kan de vergelijking worden herschikt zodat de partiële argondruk kan worden afgetrokken van de totale druk. De partiële druk van helium is dus 2, 4 atm.

mengsels van gassen: dalton's wet van partiële druk en molfracties

Tenzij individuele gassen chemisch met elkaar reageren, hebben de individuele gassen in een mengsel van gassen geen invloed op elkaars druk. Elk gas in een mengsel oefent dezelfde druk uit als het zou uitoefenen als het alleen in de container aanwezig zou zijn. De druk die door elk afzonderlijk gas in een mengsel wordt uitgeoefend, wordt de partiële druk genoemd. Dit betekent dat in een mengsel dat drie verschillende gassen A, B en C bevat, als PA de partiële druk van gas A is; PB is de partiële druk van gas B; PC is de partiële druk van gas C; dan wordt de totale druk gegeven door vergelijking 1:  <img alt="Eq1" src="https://www.jove.com/files/core/CDNSource/lessons/1038/1038_Equations-01.png" style="height: 40px;"> Dit is de wet van Dalton over de partiële druk: de totale druk van een mengsel van ideale gassen is gelijk aan de som van de partiële drukken van de samenstellende gassen. Laat nA, nB en nC het aantal mol van elk van de gassen in het mengsel zijn. Als elk gas voldoet aan de ideale gasvergelijking, kan de partiële druk worden geschreven als: <img alt="Eq2" src="https://www.jove.com/files/core/CDNSource/lessons/1038/1038_Equations-02.png" style="height: 40px;"> Omdat alle gassen dezelfde temperatuur hebben en hetzelfde volume innemen, geeft vervanging in vergelijking 1: <img alt="Eq3" src="https://www.jove.com/files/core/CDNSource/lessons/1038/1038_Equations-03.png" style="height: 40px;"> De vergelijking geeft aan dat bij constante temperatuur en constant volume de totale druk van een gasmonster wordt bepaald door het totale aantal mol aanwezig gas. Voor mengsels van gassen is het handig om een hoeveelheid in te voeren die de molfractie χ wordt genoemd en die wordt gedefinieerd als het aantal mol van een bepaalde stof in een mengsel gedeeld door het totale aantal mol van alle aanwezige stoffen. Wiskundig wordt de molfractie van stof A in een mengsel met B en C uitgedrukt als <img alt="Eq4" src="https://www.jove.com/files/core/CDNSource/lessons/1038/1038_Equations-04.png" style="height: 40px;"> Op dezelfde manier is de molfractie van B en C; <img alt="Eq5" src="https://www.jove.com/files/core/CDNSource/lessons/1038/1038_Equations-05.png" style="height: 40px;"> <img alt="Eq6" src="https://www.jove.com/files/core/CDNSource/lessons/1038/1038_Equations-06.png" style="height: 40px;"> Het combineren van de vergelijking voor de molfractie van A en de vergelijking voor partiële druk geeft: <img alt="Eq7" src="https://www.jove.com/files/core/CDNSource/lessons/1038/1038_Equations-07.png" style="height: 40px;"> De partiële druk van gas A is via zijn molfractie gerelateerd aan de totale druk van het gasmengsel. Met andere woorden: de druk van een gas in een mengsel van gassen is het product van de molfractie ervan en de totale druk van het mengsel.

Mengsels van gassen: Dalton's wet van partiële druk en molfracties

Unless individual gases chemically react with each other, the individual gases in a mixture of gases do not affect each other&rsquo;s pressure. Each gas ...

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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 each gas.

If each gas follows the ideal-gas equation, its partial pressure can be written in terms of moles, temperature, and volume. Because every gas in the mixture has the same temperature and takes up the same volume, these terms can be combined. At constant temperature and constant volume, the total pressure depends on the total number of moles of gas present.

For gas mixtures, chemists also use mole fraction, x. Mole fraction is the number of moles of one substance divided by the total number of moles in the mixture. For gas A in a mixture with B and C, the mole fractions of A, B, and C are found in this way.

Mole fraction also links directly to partial pressure. The partial pressure of gas A equals its mole fraction times the total pressure of the mixture. In other words, a gas's pressure in a mixture is its share of the total pressure.

Gas Pressure in Mixtures: Partial Pressures

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

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...

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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.

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Learn how partial pressure and mole fraction describe gas mixtures, and how Dalton's law connects each gas to the total pressure.

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Gas Pressure in Mixtures: Partial Pressures

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