Name: shifting equilibrium by changing concentration
Uploaded: 2020-09-24T15:06:50.000Z
Duration: 2 min 27 s
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Le Chatelier's Principle: Changing Concentration

Układ znajduje się w równowadze dynamicznej, gdy szybkość reakcji do przodu jest równa szybkości reakcji odwrotnej. Chociaż reakcja nadal przebiega w obu kierunkach, stężenia netto reagentów i produktów pozostają stałe.
W tym momencie, jeśli stężenie reagenta lub produktu zostanie zmienione, na przykład przez dodanie dodatkowej cząsteczki A lub usunięcie pewnej cząsteczki C, równowaga zostaje zakłócona. Takie zmiany są obciążeniem dla systemu.
Zgodnie z zasadą Le Châteliera, gdy układ w stanie równowagi jest naprężony z powodu zmiany stężenia, zmiany objętości lub ciśnienia lub zmiany temperatury, położenie równowagi przesuwa się w kierunku, aby zminimalizować naprężenia i przywrócić równowagę.
Aby zrozumieć reakcję systemu na zmiany stężenia, rozważmy dwa połączone zbiorniki na wodę, A i B. Początkowo poziom wody w obu zbiornikach jest równy, a system jest w równowadze. Następnie do zbiornika B dodaje się wodę.
Naprężenie to podnosi poziom wody w zbiorniku B i zaburza równowagę. Aby zrównoważyć to naprężenie, część wody wpływa do zbiornika A, aby przywrócić równowagę.
I odwrotnie, jeśli woda jest usuwana ze zbiornika B, obniżenie poziomu wody również wywołuje stres.
W konsekwencji woda ze zbiornika A wpływa do zbiornika B, aby przywrócić równowagę.
W przypadku układu w stanie równowagi iloraz reakcji jest równy stałej równowagi. Dodanie większej ilości reagentów do mieszaniny równowagi zmniejsza Q. Zgodnie z zasadą Le Châteliera system minimalizuje to naprężenie, przesuwając pozycję równowagi w kierunku produktów, aby zużyć dodany reagent i przywrócić równowagę. 
Podobnie, usunięcie produktu z mieszaniny równowagi doprowadzi do podobnej reakcji w celu przywrócenia równowagi.
Z kolei dodanie większej liczby produktów zwiększa Q. W ten sposób pozycja równowagi przesuwa się w kierunku reagentów, aby zużyć dodany produkt i przywrócić równowagę.
Zmiana stężenia przesuwa pozycję równowagi bez zmiany wartości K.

zasada le chateliera: zmiana koncentracji

Układ w równowadze znajduje się w stanie równowagi dynamicznej, a reakcje do przodu i do tyłu zachodzą z równą szybkością. Jeśli układ równowagi zostanie poddany zmianie warunków, która w różny sposób wpływa na te szybkości reakcji (naprężenie), wówczas szybkości nie są już równe i układ nie jest w równowadze. Następnie system doświadczy reakcji netto w kierunku większej szybkości (przesunięcia), która przywróci równowagę. Zjawisko to podsumowuje zasada Le Châteliera: jeśli układ równowagi zostanie poddany naprężeniom, w odpowiedzi na naprężenie nastąpi przesunięcie, które przywróci równowagę.

Na szybkość reakcji wpływają przede wszystkim stężenia, jak opisano w prawie szybkości reakcji, oraz temperatura, jak opisano za pomocą równania Arrheniusa. W konsekwencji zmiany stężenia i temperatury to dwa naprężenia, które mogą przesunąć równowagę.

Wpływ zmiany stężenia

Jeśli układ równowagi zostanie poddany zmianie stężenia reagenta lub produktu, zmieni się szybkość reakcji do przodu lub do tyłu. Jako przykład rozważmy reakcję równowagi:

<img alt="Eq1" src="/files/ftp_upload/11391/11391_Equation 1v2.png" style="text-align: center; height: 48px;" />

Gdy układ ten jest w równowadze, szybkości reakcji w przód i w tył są równe.

<img alt="Eq2" src="/files/ftp_upload/11391/11391_Equation 2.png" style="text-align: center; height: 50px;" />

Jeśli system jest obciążony przez dodanie reagenta, N2 lub O2, wynikający z tego wzrost stężenia powoduje wzrost szybkości reakcji w przód, przekraczając szybkość reakcji odwrotnej:

<img alt="Eq3" src="/files/ftp_upload/11391/11391_Equation 3.png" style="text-align: center; height: 50px;" />

System doświadczy tymczasowej reakcji netto w kierunku do przodu, aby przywrócić równowagę (równowaga przesunie się w prawo). Ta sama zmiana nastąpi, jeśli z układu zostanie usunięta część produktu NO, co zmniejszy szybkość reakcji odwrotnej, ponownie powodując tę samą nierównowagę szybkości.

Tę samą logikę można zastosować do wyjaśnienia przesunięcia w lewo, które wynika z usunięcia reagenta lub dodania produktu do układu równowagi. Obydwa te naprężenia powodują zwiększoną szybkość reakcji odwrotnej

<img alt="Eq4" src="/files/ftp_upload/11391/11391_Equation 4.png" style="text-align: center; height: 50px;" />

oraz tymczasowa reakcja wypadkowa w odwrotnym kierunku w celu przywrócenia równowagi.

Alternatywnie do tej interpretacji kinetycznej, wpływ zmian stężenia na równowagę można zracjonalizować w kategoriach współczynników reakcji. Kiedy układ jest w równowadze,

<img alt="Eq5" src="/files/ftp_upload/11391/11391_Equation 5.png" style="text-align: center; height: 70px;" />

Jeżeli dodamy reagent (zwiększając mianownik ilorazu reakcji) lub usuniemy produkt (zmniejszając licznik), wówczas Qc < Kc i równowaga przesunie się w prawo. Należy zauważyć, że trzy różne sposoby wywoływania tego naprężenia powodują trzy różne zmiany w składzie mieszaniny równowagowej. Jeżeli dodany zostanie N2, prawe przesunięcie spowoduje zużycie O2 i wytworzenie NO po przywróceniu równowagi, dając mieszaninę o większym stężeniu N2 i NO oraz mniejszym stężeniu O2 niż było to wcześniej. Jeśli doda się O2, nowa mieszanina równowagowa będzie miała większe stężenia O2 i NO oraz mniejsze stężenie N2. Wreszcie, jeśli NO zostanie usunięty, nowa mieszanina równowagowa będzie miała większe stężenia N2 i O2 oraz mniejsze stężenie NO. Pomimo tych różnic w składzie, wartość stałej równowagi po naprężeniu będzie taka sama jak przedtem (zgodnie z prawem działania mas). Tę samą logikę można zastosować do naprężeń związanych z usuwaniem reagentów lub dodawaniem produktu, w którym to przypadku Qc > Kc i równowaga przesunie się w lewo.

Zasada Le Chateliera: zmiana koncentracji

Układ w stanie równowagi znajduje się w stanie równowagi dynamicznej, w którym reakcje do przodu i do tyłu zachodzą w równych odstępach. Jeśli układ równowagi jest ...

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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 reactant or product can move the equilibrium in one direction or the other.

Adding a reactant, such as N2 or O2 in the example reaction, increases the forward reaction rate. The forward rate then becomes greater than the reverse rate, so the equilibrium shifts right. Removing the product NO has the same effect because it lowers the reverse reaction rate and creates the same imbalance.

The opposite changes cause a left shift. Removing reactant or adding product increases the reverse reaction rate compared with the forward rate. The system then moves in the reverse direction until equilibrium is reached again.

This shift can also be explained with the reaction quotient, Qc, and the equilibrium constant, Kc. When reactant is added, Qc becomes less than Kc. When product is removed, Qc also becomes less than Kc, so the equilibrium shifts right. If reactant is removed or product is added, then Qc is greater than Kc and the equilibrium shifts left.

Although the final composition changes, the equilibrium constant stays the same after the stress is removed and the system rebalances. If N2 is added, the new mixture has more N2 and NO and less O2. If O2 is added, the mixture has more O2 and NO and less N2. If NO is removed, the mixture ends with more N2 and O2 and less NO. The same idea applies to shifts caused by removing reactant or adding product.

Shifting Equilibrium by Changing Concentration

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le chatelier's principle: 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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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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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 concentration shifts chemical equilibrium, including why adding or removing reactants or products moves the reaction left or right.

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Shifting Equilibrium by Changing Concentration

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