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Change in temperature's effect on K

Posted: Mon Jan 21, 2019 12:32 pm
by Katherine Grillo 1B
I'm confused as to why heating will favor R formation if the reaction is exothermic. If the reaction releases heat, wouldn't the extra heat favor P formation?

Re: Change in temperature's effect on K

Posted: Mon Jan 21, 2019 12:48 pm
by Jesse Kuehn 1B
I always get confused about this too. Usually, I think of an endothermic reaction that is taking in energy where two atoms or molecules are being joined. These molecules need energy in order to be joined so the more heat you apply, the more products will be made. And then I just think that an exothermic reaction is the opposite of this. You might also think that an exothermic reaction is releasing heat so adding more would inhibit this release and less product would be made. I agree, it is confusing

Re: Change in temperature's effect on K

Posted: Mon Jan 21, 2019 12:57 pm
by Fayez Kanj
Hello!

Le Chatelier's Principle says that if a chemical equilibrium is subject to change, the equilibrium position will shift so as to minimize the effect of the change.

When heating a reaction:

The new equilibrium position will shift to the endothermic side, so as to absorb/use up all that extra heat, whether that be the forward or reverse reaction

When cooling a reaction:

The new equilibrium position will shift to the exothermic side to increase heat release and restore the higher initial temperature


Hope this helps :)

Re: Change in temperature's effect on K

Posted: Mon Jan 21, 2019 2:57 pm
by George Ghaly 2L
If the reaction is endothermic then increasing the heat would favor an equilibrium sitting to towards the product. Decreasing the heat would favor an equilibrium sitting towards the reactants. For exothermic the process is reversed as expected.

Re: Change in temperature's effect on K

Posted: Mon Jan 21, 2019 3:14 pm
by Joanna Pham - 2D
To remember which direction the reaction will favor if the reaction is endothermic or exothermic, I like to have a visual in mind.

If the reaction is endothermic, that means the reaction requires heat to form its products. So in the chemical equation, on the side of the reactants, heat should be added. Thus, because heat is being added to the left side of the arrows, then the reaction will favor the right side of the arrows (the products) to minimize the change based on Le Chatelier's principle. If Professor Lavelle gives a conceptual question on the exam and there's no chemical equation, I like to visualize this in my head to help me remember which direction will be favored:

It'll be the opposite if it's an exothermic reaction. Heat will be released during the reaction, so to minimize the effects, the reaction will favor the reactants: