Effect of Heat on equilibrium

[Synapsis]

I understand that the only thing that will change the value of K is temperature, but I just need a quick clarification.

One thing that we learned in GChem was that if you increase temperature for an endothermic reaction (for example), you get more products. Now, is the K value changed, and that's what's causing us to get more products, or this Le Chatelier's at work?

I'm confused because I know (from TBR) that changing temperature counts as an external stress. And Le Chatelier's says that following an external stress, you move back toward equilibrium. At least superficially, the concepts seem to contradict each other by their wording. Are we changing the position of the equilibrium or are we moving back to reestablish it? Could we be doing both at the same time?

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[brood910]

Endothermic means

"q" is on the reactant side.

So, if you increase the temperature, "q" will increase, and thus, more products will be formed, following Le Chatelier.

 

[Synapsis]

Endothermic means

"q" is on the reactant side.

So, if you increase the temperature, "q" will increase, and thus, more products will be formed, following Le Chatelier.

Right, I get that already. I'm just confused with how it relates to the fact that changing temperature changes the equilibrium constant. How could temperature change the equilibrium constant if Le Chatelier's is acting to move us back toward equilibrium?

 

[brood910]

It is beyond what you need to know for MCAT.

You just need to know that K can be only changed by T changes, as you already know.

 

[Synapsis]

It is beyond what you need to know for MCAT.

You just need to know that K can be only changed by T changes, as you already know.

Okay, I kind of suspected that a combination of those two topics was a bit advanced anyway. Thanks!

 

[AureatEagle]

Okay, I kind of suspected that a combination of those two topics was a bit advanced anyway. Thanks!

This is a fantastic question, and even though it's a bit advanced, I think it's still worth understanding. Imagine we start out with an endothermic reaction where Q = K. What ends up happening is by changing T, you actually end up changing K, not Q-- just as you would expect since we know that T changes K. As a result of the increased T, the K for the reaction increases, such that you will see more products once the reaction comes to equilibrium. Now that K has increased, the Q from where we began is now smaller than K (Q<K), and the reaction will proceed forward as we know it will whenever Q < K.

Hope that helps!

 

[Synapsis]

This is a fantastic question, and even though it's a bit advanced, I think it's still worth understanding. Imagine we start out with an endothermic reaction where Q = K. What ends up happening is by changing T, you actually end up changing K, not Q-- just as you would expect since we know that T changes K. As a result of the increased T, the K for the reaction increases, such that you will see more products once the reaction comes to equilibrium. Now that K has increased, the Q from where we began is now smaller than K (Q<K), and the reaction will proceed forward as we know it will whenever Q < K.

Hope that helps!

That makes complete sense. Thank you!