# Why does the equilibrium constant vary only with temperature?

• quantumlight
In summary, the equilibrium constant varies with temperature due to changes in the rate constants, solids and liquids have a minimal effect on the rate equations, 1 atm is the standard condition, and the presence of noble gases can affect the collision frequency and thus the rate dynamics.
quantumlight
why does the equilibrium constant vary only with temperature?

and why is pure substances like solids and liquids not count toward the equilibirum equation?

why do you have to have a reference pressure of 1 atm? (i know this is to take away the units but does this hav a logical function other than that? how does this affect the equation?)

can noble gases affect the equilibrium? (i think it shouldn't since the partial pressure of the original reactants would still be the same)

The policy here at PF is that you show your approach to the question before any of us are allowed to help you. However, the questions you have asked in particular are commonly asked by students outside their homework endeavors and thus I shall offer an brief explanation. An appropriate explanation for all of these questions entails several mathematical derivations and the related assumptions, all of this can be found in a standard Physical Chemistry text e.g. Physical Chemistry by Atkins.

Your text should offer a short explanation on why the equilibrium constants of some reactions in water is altered by temperature, in short, all of it stems from the relative changes in the forward and reverse rate constants for a simple reaction mechanism. Also, the rate constants are thermodynamically based, as it is associated with the activations energies for the forward and reverse reactions respectively.

Liquids and solids technically do count, to a very small degree, towards the rate equations, however they are mathematically insignificant in influencing the rate parameters.

1 atm is the standard condition.

The presence of any gas would affect the collision frequency of the analyte and thus would affect the rate dynamics.

The equilibrium constant, K, is a measure of the ratio of products to reactants at equilibrium. It is a constant value at a given temperature, but can change with changes in temperature. This is because temperature affects the energy of the reactants and products, which in turn affects their rates of reaction. This can lead to a shift in the equilibrium position, resulting in a change in the equilibrium constant.

Pure substances like solids and liquids do not affect the equilibrium equation because they are not included in the equilibrium expression. This is because their concentrations do not change significantly during a reaction, and therefore do not have an impact on the equilibrium position.

The reference pressure of 1 atm is used to take away the units in the equilibrium constant expression, as you mentioned. However, it also has a logical function in that it is a standardized pressure that is commonly used in laboratory experiments. This allows for easier comparison and communication of results between different experiments.

Noble gases do not affect the equilibrium because they do not participate in the reaction. Their presence in the system does not change the partial pressures of the original reactants, as you mentioned. Therefore, they do not have an impact on the equilibrium position or the equilibrium constant.

## 1. Why is temperature the only factor that affects the equilibrium constant?

Temperature is the only factor that affects the equilibrium constant because it directly influences the energy of the reactants and products in a chemical reaction. As temperature increases, the molecules have more kinetic energy and collide more frequently, leading to more successful reactions and a shift towards equilibrium.

## 2. How does temperature affect the equilibrium constant?

As temperature increases, the equilibrium constant also increases. This is because the forward reaction becomes more favorable and the reverse reaction becomes less favorable. In other words, the equilibrium shifts towards the products side at higher temperatures.

## 3. Does the equilibrium constant change at different temperatures?

Yes, the equilibrium constant changes at different temperatures. As mentioned before, the equilibrium constant increases with higher temperatures, and decreases with lower temperatures. This is because the reaction rate is affected by temperature, and the equilibrium constant is a representation of the ratio of the forward and reverse reaction rates.

## 4. Can the equilibrium constant be calculated at any temperature?

Yes, the equilibrium constant can be calculated at any temperature. However, the values used in the calculation must be adjusted to account for the change in temperature. This is usually done through the use of the Van't Hoff equation, which relates the equilibrium constant at two different temperatures.

## 5. Why is it important to consider temperature when calculating the equilibrium constant?

It is important to consider temperature when calculating the equilibrium constant because it affects the direction and extent of a chemical reaction. Temperature changes can significantly alter the value of the equilibrium constant, and understanding this relationship is crucial in predicting and controlling chemical reactions.

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