Temperature and the equilibrium constant

[member 392791]

The equilibrium constant changes with a change in temperature, I am confused as to the directions and why Qc is behaving oppositely of what I think it does

For example, my textbook says a temperature increase favors an endothermic reaction (left to right) and a temperature decrease favors the exothermic direction (from right to left). This is ambiguous to me, I am not sure what they mean by favor, if somone can clarify.

Anyway, here is an endothermic reaction

heat + A ⇔ B + C

If you increase the temperature, the heat is treated as a reactant and it shifts from left to right, that is fine

Exothermic:

A + B ⇔ C + heat
decrease the temperature, shouldn't this shift from left to right, since the heat is treated like a concentration and it is taken away, so to make up for it more is going from left to right, yet the book says right to left.


My other concern is how the equilibrium constant changes with temperature. We had a worksheet and its says heating an endothermic equilibrium system increases K. The answer given is true, and I have 2 thoughts on this.

The first is that if you have an endothermic reaction, heating it up increases the number of the reactant side, so the denominator is bigger and K is lower. However, if you increase the temperature, equilibrium would shift to the right so now the numerator is bigger, and therefore K is bigger. I think the second statement is the correct one, but just want to confirm.

It says cooling an exothermic equilibrium increases K. That mens equilibrium shifts to the right (which contradicts my textbook from above) and the numerator is now bigger, so K is bigger.

 

[pa5tabear]

Exothermic:

A + B ⇔ C + heat
decrease the temperature, shouldn't this shift from left to right, since the heat is treated like a concentration and it is taken away, so to make up for it more is going from left to right, yet the book says right to left.

No, it should be favoring the products (shifting right to left). Heat is not exactly the same thing as temperature. If temperature is decreased, heat is leaving the system. The system will "maintain" its temperature by reacting to the product side to release heat.

Right ----> Left

Le Chatelier's principle.

 

[member 392791]

Maybe we're reading this different, but if its favoring the products, you are saying some of the reactants are going to go to the product side. The reactants are on the left, and the products are on the right. Therefore, reactants (left) to products (right)?

Right -----> Left is backwards, my right hand is on the side where you have written left

Left -----> Right should be how you wrote it, no?

 

[pa5tabear]

Maybe we're reading this different, but if its favoring the products, you are saying some of the reactants are going to go to the product side. The reactants are on the left, and the products are on the right. Therefore, reactants (left) to products (right)?

Right -----> Left is backwards, my right hand is on the side where you have written left

Left -----> Right should be how you wrote it, no?

Hahah I just realized that I did write it incorrectly. I apologize.

Products are definitely favored in an exothermic reaction when temperature is decreased.

 

[LudusRex]

I can understand your confusion. Temperature and the equilibrium constant are closely related, and it can be confusing to understand their behavior.

First, let's clarify what is meant by "favoring" a direction in a reaction. When we say that increasing temperature favors an endothermic reaction, it means that the equilibrium will shift towards the products (right side of the equation) as more heat is added. This is because endothermic reactions absorb heat, so increasing the temperature provides more energy for the reaction to proceed in the forward direction.

On the other hand, decreasing temperature favors an exothermic reaction because the equilibrium will shift towards the reactants (left side of the equation) as heat is removed. This is because exothermic reactions release heat, so decreasing the temperature will slow down the reaction and shift the equilibrium towards the reactants.

Now, let's address your concerns about the equilibrium constant changing with temperature. You are correct in your understanding that increasing the temperature of an endothermic reaction will shift the equilibrium towards the products, making the numerator larger and increasing the value of K. Similarly, decreasing the temperature of an exothermic reaction will shift the equilibrium towards the products, also increasing the value of K.

In terms of the statements given in your worksheet, they are both correct. Heating an endothermic reaction will increase K because the equilibrium will shift towards the products, making the numerator larger. Cooling an exothermic reaction will also increase K because the equilibrium will shift towards the products, making the numerator larger.

I hope this helps clarify your understanding of temperature and the equilibrium constant. It's important to remember that these concepts are closely intertwined and can be a bit tricky to grasp at first. Keep asking questions and seeking clarification, and you will continue to deepen your understanding of these important scientific principles.