Name: relating kc and kp in gas equilibria
Uploaded: 2020-09-24T15:06:50.000Z
Duration: 2 min 15 s
Channel: JoVE

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Chemistry

Matter and its Interactions

PS.Chm.5.2

homogeneous-equilibria-for-gaseous-reactions

Homogeneous Equilibria for Gaseous Reactions

Voor chemische reacties, waarbij de reactanten en producten allemaal gassen zijn, kan de evenwichtsconstante ook worden berekend met behulp van de individuele partiële drukken in plaats van hun molaire concentraties. Dus wanneer gassen A en B in een omkeerbare reactie worden omgezet in gassen C en D, kan de evenwichtsuitdrukking in plaats daarvan worden geschreven als de partiële druk van elk gas, verhoogd tot hun stoichiometrische coëfficiënten. De evenwichtsconstante wordt aangeduid als Kp, waarbij het onderschrift p de druk aangeeft.Voor een gegeven gasvormige reactie is Kp niet noodzakelijk gelijk aan Kc, omdat de partiële druk van een gas en zijn molaire concentratie afzonderlijke waarden zijn. Er kan echter een verband worden afgeleid tussen de twee constanten met behulp van de ideale gasvergelijking en de definitie van molariteit. Om dit verband af te leiden, moet u de evenwichtsuitdrukkingen voor Kc en Kp voor de gegeven chemische reactie beschouwen.De ideale gasvergelijking relateert de druk van een gas aan het aantal mol en het volume bij een bepaalde temperatuur. Door de molariteitsverhouding tot het volume in de ideale gasvergelijking te vervangen, kan de druk van een ideaalgas worden uitgedrukt in termen van zijn molaire concentratie. Op deze manier kunnen de individuele partiële drukken in de uitdrukking voor Kp worden vervangen door het concentratie-equivalent van elk gas.De stoichiometrische coëfficiënten blijven ongewijzigd. In de gemodificeerde uitdrukking van Kp kan de verhouding van de concentratie van de producten tot de concentratie van reactanten worden vervangen door Kc.Deze vergelijking geeft de relatie tussen de twee constanten Kp is gelijk aan Kc maal RT verhoogd tot de som van de coëfficiënten van de producten min de som van de coëfficiënten van de reactanten. Het verschil tussen de coëfficiënten van gasvormige reactanten en producten kan worden weergegeven als delta n.

homogene evenwichten voor gasreacties

Homogene evenwichten voor gasreacties Voor gasfasereacties kan de evenwichtsconstante worden uitgedrukt in termen van de molaire concentraties (Kc) of de partiële druk (Kp) van de reactanten en producten. Een verband tussen deze twee K-waarden kan eenvoudigweg worden afgeleid uit de ideale gasvergelijking en de definitie van molariteit. Volgens de ideale gasvergelijking: <img alt="Eq1" src="/files/ftp_upload/11387/11387_Equation_1.png" style="text-align: center; height: 50px;"> De molaire concentratie of molariteit wordt gegeven door het aantal mol gedeeld door het volume: <img alt="Eq2" src="/files/ftp_upload/11387/11387_Equation_2.png" style="text-align: center; height: 100px;"> Dus, <img alt="Eq3" src="/files/ftp_upload/11387/11387_Equation_3.png" style="text-align: center; height: 90px;"> waarbij P de partiële druk is, V het volume is, n het aantal mol is, R de gasconstante is, T de temperatuur is en M de molaire concentratie is. Voor de gasfasereactie: m A + n B ⇌ x C + y D <img alt="Eq4" src="/files/ftp_upload/11387/11387_Equation_4.png" style="text-align: center; height: 130px;"> En dus is de relatie tussen Kc en KP hetzelfde <img alt="Eq5" src="/files/ftp_upload/11387/11387_Equation_5.png" style="text-align: center; height: 50px;"> waarbij Δn het verschil is in de molaire hoeveelheden product- en reactantgassen, in dit geval: <img alt="Eq6" src="/files/ftp_upload/11387/11387_Equation_6.png" style="text-align: center; height: 50px;"> Deze tekst is aangepast van <a href="https://openstax.org/books/chemistry-2e/pages/13-2-equilibrium-constants">Openstax, Chemistry 2e, Sectie 13.2 Evenwichtsconstanten</a>.

Homogene evenwichten voor gasreacties

Homogeneous Equilibria for Gaseous Reactions
For gas-phase reactions, the equilibrium constant may be expressed in terms of either the molar ...

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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 temperature. Molar concentration is written as M.

For a gas reaction written as mA + nB ⇌ xC + yD, the two equilibrium constants are connected by a simple relation. That relation depends on Δn, which is the difference between the molar amounts of gaseous products and gaseous reactants. This connection helps show how Kc and Kp describe the same equilibrium in different ways.

Relating Kc and Kp in Gas Equilibria

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

le-chatelier-s-principle-changing-concentration

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...

homogeneous equilibria for gaseous reactions

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...

reaction quotient

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...

calculating equilibrium concentrations

Equilibrium Concentrations from an ICE Table

Equilibrium concentrations can be found from initial concentrations and an equilibrium constant. This skill matters in many areas of science and technology, including pharmaceutical product formulation and dosing. After a drug is ingested or injected, it may take part in several chemical equilibria that change its final concentration in the body system of interest. Scientists use these quantitative equilibrium relationships to help calculate a dosage that will produce the desired therapeutic...

dynamic equilibrium

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)

le-chatelier-s-principle-changing-volume-pressure

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...

le chatelier's principle: changing temperature

le-chatelier-s-principle-changing-temperature

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...

the small x assumption

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.

key terms and concepts

Learn how gas-phase equilibrium constants are connected by the ideal gas law. Compare Kc and Kp using molarity, partial pressure, and Δn.

Relating Kc and Kp in Gas Equilibria | JoVE K12

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Relating Kc and Kp in Gas Equilibria

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