Name: gas equilibrium under volume changes
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Le Chatelier's Principle: Changing Volume (Pressure)

Het principe van Le Châtelier kan worden gebruikt om te voorspellen hoe een systeem in evenwicht zou reageren op de spanning van een verandering in volume of druk. Het volume van een gas is omgekeerd evenredig met zijn druk;daarom verhoogt een afname van het volume voor een systeem in evenwicht de druk en verstoort het het evenwicht. Als reactie daarop zal de evenwichtspositie in een richting verschuiven om de spanning te minimaliseren.De ideale gaswet stelt dat de druk van een gas recht evenredig is met het aantal mol. De richting van de verschuiving die nodig is om het evenwicht te herstellen is dus afhankelijk van het aantal mol gasdeeltjes aan weerszijden van de reactie. Omdat meer mol gas resulteert in een hogere druk, verschuift een toename van de druk de evenwichtspositie naar de kant met minder mol om de druk te verlagen.Evenzo verschuift een afname van de druk de evenwichtspositie naar de kant met meer molen gas. Overweeg een chemisch evenwicht, waarbij één mol gasvormig fosforpentachloride uiteenvalt in één mol fosfortrichloride en één mol chloorgas in totaal twee mol product. Als de zuiger naar beneden wordt gedrukt, neemt het volume van het evenwichtssysteem af, waardoor de druk toeneemt.Dit verstoort het evenwicht en resulteert in Q groter dan K.Dus verschuift de evenwichtspositie naar de reactanten, met minder molen gasdeeltjes, om de druk te verlagen en het evenwicht te herstellen. Omgekeerd verhoogt het omhoog trekken van de zuiger het volume en verlaagt de druk. In dit geval wordt Q kleiner dan K.Om de druk te verhogen, verschuift de evenwichtspositie naar de producten, de kant met de meeste molen gas, en herstelt het evenwicht.Het verhogen van de druk door een inert gas toe te voegen aan een evenwichtsmengsel bij constant volume, heeft geen invloed op het evenwicht omdat de partiële drukken van de gasvormige reactanten en producten ongewijzigd blijven. Voor evenwichtssystemen met een gelijk aantal mol gasvormige reactanten en producten, zoals de reactie tussen jodiumgas en chloorgas om jodiummonochloride te produceren, zal een verandering in het volume van het systeem geen effect hebben op het evenwicht.

principe van le chatelier: volume (druk) veranderen

Voor gasfase-evenwichten kunnen veranderingen in de concentraties van reactanten en producten optreden bij gewijzigd volume en druk. De partiële druk, P, van een ideaal gas is evenredig met zijn molaire concentratie, M. <img alt="Eq1" src="/files/ftp_upload/11392/11392_Equation 1.png" style="text-align: center; height: 70px;"> Veranderingen in de partiële druk van een reactant of product zijn dus in wezen veranderingen in concentraties; daarom hebben deze veranderingen dezelfde effecten op de evenwichten. Naast het toevoegen of verwijderen van reactanten of producten, kunnen de drukniveaus (concentraties) van soorten in een gasfase-evenwicht ook worden gewijzigd door het volume dat door het systeem wordt ingenomen te veranderen. Omdat alle soorten met een gasfase-evenwicht hetzelfde volume innemen, zal een gegeven volumeverandering dezelfde verandering in concentratie veroorzaken voor zowel reactanten als producten. Om te bepalen welke verschuiving dit soort stress eventueel teweeg zal brengen, moet rekening worden gehouden met de stoichiometrie van de reactie. Bij evenwicht wordt de reactie N2 (g) + O2 (g) ⇌ 2 NO (g) beschreven door het reactiequotiënt <img alt="Eq2" src="/files/ftp_upload/11392/11392_Equation 2.png" style="text-align: center; height: 70px;"> Als het volume dat wordt ingenomen door een evenwichtsmengsel van deze soorten met een factor 3 wordt verminderd, zal de partiële druk van alle drie de soorten met een factor 3 toenemen: <img alt="Eq3" src="/files/ftp_upload/11392/11392_Equation 3.png" style="text-align: center; height: 70px;"> En dus resulteert het veranderen van het volume van dit gasfase-evenwichtsmengsel niet in een verschuiving van het evenwicht. Een soortgelijke behandeling van een ander systeem, 2 SO2 (g) + O2 (g) ⇌ 2 SO3 (g), levert echter een ander resultaat op: <img alt="Eq4" src="/files/ftp_upload/11392/11392_Equation 4.png" style="text-align: center; height: 200px;"> In dit geval resulteert de verandering in volume in een reactiequotiënt dat kleiner is dan de evenwichtsconstante, en dus zal het evenwicht naar rechts verschuiven. Deze resultaten illustreren de relatie tussen de stoichiometrie van een gasfase-evenwicht en het effect van een door volume geïnduceerde druk(concentratie)verandering. Als de totale molaire hoeveelheden reactanten en producten gelijk zijn, zoals in het eerste voorbeeld, verschuift een verandering in volume het evenwicht niet. Als de molaire hoeveelheden reactanten en producten verschillend zijn, zal een verandering in volume het evenwicht verschuiven in een richting die de volumeverandering beter ‘accommodeert’. In het tweede voorbeeld levert drie mol reactant (SO2 en O2) twee mol product (SO3) op, en dus zorgt het verkleinen van het systeemvolume ervoor dat het evenwicht naar rechts verschuift, omdat de voorwaartse reactie minder gas (2 mol) produceert dan de omgekeerde reactie. (3mol). Omgekeerd zou het vergroten van het volume van dit evenwichtssysteem resulteren in een verschuiving naar reactanten. Deze tekst is aangepast van <a href="https://openstax.org/books/chemistry-2e/pages/13-3-shifting-equilibria-le-chateliers-principle">Openstax, Chemistry 2e, Sectie 13.3 Verschuivende Evenwichten: LeChateliers Principe</a>.

Principe van Le Chatelier: volume (druk) veranderen

For gas-phase equilibria, changes in the concentrations of reactants and products can occur with altered volume and pressure. The partial pressure, P, of ...

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gas equilibrium under volume changes

Gas-phase equilibrium can shift when the volume of the system changes. In these reactions, a change in pressure changes concentration because the partial pressure of an ideal gas is proportional to its molar concentration. That means pressure changes affect equilibrium in the same way as concentration changes.

When the volume of a gas mixture changes, the concentrations of reactants and products change together. Since every gas in the equilibrium occupies the same space, the same volume change affects each species in the same way. To predict whether the equilibrium shifts, you must look at the reaction stoichiometry.

For the equilibrium N2(g) + O2(g) ⇌ 2 NO(g), decreasing the volume by a factor of 3 increases the partial pressures of all three gases by a factor of 3. In this case, the reaction quotient still matches the equilibrium position, so the equilibrium does not shift. The total moles of reactants and products are equal, and that is why the volume change has no effect.

A different result appears for 2 SO2(g) + O2(g) ⇌ 2 SO3(g). Here, decreasing the volume makes the reaction quotient smaller than the equilibrium constant, so the equilibrium shifts right. Three moles of reactant form two moles of product, so the forward reaction makes less gas. Increasing the volume would shift this system toward the reactants.

Gas Equilibrium Under Volume Changes

the equilibrium constant

Chemical Equilibrium and Kc Rules

Chemical equilibrium and the equilibrium constant Kc describe how reactants and products are balanced in a reaction. In the oxidation of sulfur dioxide, a mixture that starts with reactants only has no product at first. As the reaction moves forward toward equilibrium, reactant concentrations decrease and product concentration increases. When equilibrium is reached, the concentrations of both stay constant. A reaction can also begin with only products present. In that case, the reaction moves...

le chatelier's principle: changing concentration

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Shifting Equilibrium by Changing Concentration

Chemical equilibrium is a dynamic balance. At equilibrium, the forward and reverse reactions happen at equal rates. If the system is stressed in a way that changes one rate more than the other, it is no longer at equilibrium and will shift until balance is restored. This behavior is described by Le Châtelier’s principle. Changes in concentration are a major stress on an equilibrium system. Reaction rates depend mainly on concentration and temperature. For that reason, changing the amount of a...

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Relating Kc and Kp in Gas Equilibria

Gas-phase equilibrium can be written using either concentration or pressure. The equilibrium constant may be shown as Kc, which uses molar concentration, or as Kp, which uses partial pressure of the reactants and products. The link between Kc and Kp comes from the ideal gas equation and the definition of molarity. Molarity is the number of moles divided by volume. In the ideal gas equation, P stands for partial pressure, V for volume, n for number of moles, R for the gas constant, and T for...

calculating the equilibrium constant

Finding Kc from Equilibrium Data

The equilibrium constant, Kc, can be found from the equilibrium concentrations of reactants and products. When those concentrations are known, the calculation is straightforward. The values are placed into the Kc expression for the reaction. One example uses nitrogen dioxide and dinitrogen tetroxide. When 0.10 mol NO2 is added to a 1.0-L flask at 25 °C, the concentrations change until equilibrium is reached. At equilibrium, [NO2] is 0.016 M and [N2O4] is 0.042 M, and these values are used to...

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Using Q to Track Equilibrium Changes

Reaction quotient Q helps track how far a reversible reaction has moved toward equilibrium. For a balanced reaction such as m A + n B ⇌ x C + y D, Q comes directly from the stoichiometric coefficients in the equation. When concentrations are used, the expression is written as Qc. For gases, a similar form uses partial pressures. These expressions use relative concentration and pressure values, not absolute values. That means reaction quotients are dimensionless and have no units. As a reaction...

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Equilibrium Concentrations from an ICE Table

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Chemical Equilibrium in Reversible Reactions

Chemical equilibrium in reversible reactions happens when a reaction moves in both directions at the same time. A reversible reaction uses a double arrow to show that products can turn back into reactants. At equilibrium, the concentrations of reactants and products stay constant over time because the forward and reverse reaction rates are equal. The video uses the reversible decomposition of colorless dinitrogen tetroxide to brown nitrogen dioxide as an example. At time zero, there is finite...

le chatelier's principle: changing volume (pressure)

Gas-phase equilibrium can shift when the volume of the system changes. In these reactions, a change in pressure changes concentration because the partial pressure of an ideal gas is proportional to its molar concentration. That means pressure changes affect equilibrium in the same way as concentration changes. When the volume of a gas mixture changes, the concentrations of reactants and products change together. Since every gas in the equilibrium occupies the same space, the same volume change...

le chatelier's principle: changing temperature

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Le Chatelier's Principle in Heating and Cooling

Le Chatelier's principle helps explain how chemical equilibrium responds to heating and cooling. A system at equilibrium will shift to restore balance after a temperature change, but the equilibrium constant, K, will not stay the same. Instead, the mixture reaches a new equilibrium with a different composition. This temperature effect is different from a concentration change, which shifts equilibrium without changing K. To understand why temperature matters, the reaction can be written with...

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Estimating Equilibrium with Small Changes

A small equilibrium constant can make equilibrium calculations easier. In these reactions, the equilibrium position favors the reactants. When the initial reactant concentration is high and the Kc value is small, the change in concentration may be negligible. In that case, the equilibrium concentration is close to the initial concentration. This idea helps simplify weak acid and weak base problems. Chemists can assume that some equilibrium concentrations are equal to the initial concentrations.

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Learn how changing volume changes pressure and concentration in gas-phase equilibrium, and why stoichiometry decides whether the system shifts left or right.

Gas Equilibrium Under Volume Changes | JoVE K12

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Gas Equilibrium Under Volume Changes

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