Understanding Keq: Effects of Concentration Changes on Equilibrium

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In summary, the equilibrium constant (Keq) is a constant value that is determined by the ratio of the rate constants and thermodynamic parameters involved in a reaction. It is dependent on temperature and is considered constant as long as the temperature remains constant.
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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.
 
  • #3
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.
 
  • #4
so the Keq never changes? not even by 0.0000000001?
 
  • #5
It depends on temperature. If the temperature is constant, then the keq doesn't change. Its just that. A constant.
 
  • #6
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.
 

FAQ: Understanding Keq: Effects of Concentration Changes on Equilibrium

What is Keq and how is it calculated?

Keq, also known as the equilibrium constant, is a measure of the extent of a chemical reaction at equilibrium. It is calculated by taking the ratio of the products' concentrations to the reactants' concentrations, with each concentration raised to the power of its coefficient in the balanced chemical equation.

How is Keq affected by changes in concentration, pressure, and temperature?

Changes in concentration, pressure, and temperature can all affect the value of Keq. An increase in concentration of reactants will shift the equilibrium to the right, resulting in a higher Keq value. Increased pressure will also shift the equilibrium to the side with fewer moles of gas, resulting in a higher Keq value. Temperature changes can either increase or decrease Keq, depending on whether the reaction is exothermic or endothermic.

What does a high or low Keq value indicate?

A high Keq value indicates that the reaction is product-favored, meaning there is a larger amount of products at equilibrium. A low Keq value indicates that the reaction is reactant-favored, meaning there is a larger amount of reactants at equilibrium. Keq values closer to 1 indicate that the reaction is balanced, with similar amounts of products and reactants at equilibrium.

Can Keq be used to predict the direction of a reaction?

Yes, the value of Keq can be used to predict the direction of a reaction. If Keq is greater than 1, the reaction will proceed to the right and produce more products. If Keq is less than 1, the reaction will proceed to the left and produce more reactants. If Keq is equal to 1, the reaction is at equilibrium and will not proceed in either direction.

How does Keq differ from Kc and Kp?

Kc and Kp are specific types of equilibrium constants that are used for reactions in solution and in gases, respectively. Keq is a general term that can be used for any type of equilibrium, including reactions in solution and in gases. Kc is calculated using concentrations, while Kp is calculated using partial pressures. Keq is calculated using either concentrations or partial pressures, depending on the type of reaction.

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