Understanding Keq: Effects of Concentration Changes on Equilibrium

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Discussion Overview

The discussion revolves around the concept of the equilibrium constant (Keq) in chemical reactions, particularly focusing on how changes in the concentration of reactants or products affect Keq. Participants explore theoretical implications, definitions, and the relationship between concentration changes and equilibrium shifts, with references to thermodynamic parameters.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants assert that changing the concentration of reactants or products causes the system to re-shift, but the equilibrium constant (Keq) remains unchanged.
  • One participant questions whether Keq might change slightly when reactant concentrations do not return fully to their original values after a shift.
  • Another participant emphasizes that for Keq to remain constant, reactant concentrations cannot return to their original values unless there is an infinite supply of products.
  • It is noted that the equilibrium constant is defined as constant if the temperature remains constant.
  • A participant introduces the idea that Keq can be derived from the ratio of rate constants and is linked to thermodynamic parameters, suggesting a connection to Gibbs free energy.
  • There is an acknowledgment of a lack of direct connections between thermodynamic parameters and quantum mechanical descriptions regarding Keq.

Areas of Agreement / Disagreement

Participants express differing views on whether Keq can change slightly due to concentration changes, with some maintaining that it is constant under certain conditions, while others question this assertion. The discussion remains unresolved regarding the nuances of how concentration changes relate to Keq.

Contextual Notes

Participants reference the importance of temperature in determining the constancy of Keq, but there are unresolved assumptions regarding the implications of concentration changes and the definitions involved.

Fusilli_Jerry89
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I have read in many places that if you change the concentration of reactants or products in an equilibrium equation, that it re-shifts, and the keq doesn't change. However, doesn't it change, but just ever so slightly? Because when you remove a reactant, yes that reactants concentration does go back up, but no completely back to its original concentration, so wouldn't the Keq have to change ever so slightly?
 
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By definition the equilibrium constant is... constant.
 
Fusilli_Jerry89 said:
I have read in many places that if you change the concentration of reactants or products in an equilibrium equation, that it re-shifts, and the keq doesn't change. However, doesn't it change, but just ever so slightly? Because when you remove a reactant, yes that reactants concentration does go back up, but no completely back to its original concentration, so wouldn't the Keq have to change ever so slightly?
No, you've misunderstood. For K to be constant, the reactant concentration can not go back up to its original value (unless there's an infinite supply of the product). The reactant concentration goes back up some (but not all the way, so it is less than before), and the product is also decreased (in order to remake some of the reactant). The appropriate ratio is a constant.
 
so the Keq never changes? not even by 0.0000000001?
 
It depends on temperature. If the temperature is constant, then the keq doesn't change. Its just that. A constant.
 
Fusilli_Jerry89 said:
I have read in many places that if you change the concentration of reactants or products in an equilibrium equation, that it re-shifts, and the keq doesn't change. However, doesn't it change, but just ever so slightly? Because when you remove a reactant, yes that reactants concentration does go back up, but no completely back to its original concentration, so wouldn't the Keq have to change ever so slightly?

The equilibrium constant can be derived from the ratio of the rate constants that are involved in the particular reaction, it is also linked to the thermodynamic parameters, such as the standard Gibb's, in association with the reaction.

Although I'm not aware of any direct connections between thermodynamic parameters and quantum mechanical descriptions, the equilibrium constant may be predictable and is deemed constant with respect to a specified temperature.
 

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