Effect of Temperature on Kc

[005995461]

Hi, I just had a question on the relationship between temperature and Kc. How does the enthalpy change of the reaction affect it's equilibrium constant?

[Jocelyn Ni 3C]

If the reaction is endothermic, an increase in energy would increase the K value, favoring the production of product. If the reaction is exothermic, an increase in energy would decrease the K value, favoring the production of reactant.

[Andrew Nguyen 3L]

I see the enthalpy of the reaction like another product or reactant. If a rxn is exothermic, it is released in the products. If a rxn is endothermic, it is used in the reactants. An increase in temperature is like increasing the heat in the products or reactants.

[Mallika Mathew]

I like to think of it as when temperature increases, the side with higher enthalpy is favored and when temperature decreased the side with lower enthalpy is favored. So therefore, when they say temperature increases, for an endothermic reaction the products which have higher enthalpy will be favored and for an exothermic reaction the reactants which have higher enthalpy will be favored. It would be the opposite for a temperature decrease.

[Ben Hsieh 3I]

Yes, depending on the type of reaction whether exothermic or endothermic. Heat is a product or reactant respectively and the same conditions under Le Chatelier's principle apply.

[John_Sunthorn_3B]

To be more conceptual, if a reaction is exothermic (which is when deltaH is negative), that means heat is being released as reactant goes to product. However, for product to go back into reactant (as it would have to happen in equilibrium), you would need to use heat in order to turn product into reactant. At equilibrium, it's important to remember that it is not only in equilibrium in terms of concentrations, but in terms of heat; the amount of heat (which is the temperature) of the system will stay the same at equilibrium. However, if you were to raise that temperature, what happens then is that there is "too much" heat in the system, and it would want to go back down in order to return to equilibrium. However, the reaction will ultimately end up with more reactant than product, as increasing the temperature favors the formation of reactant from product, as that itself is a process that uses energy (as this is the reverse reaction of an exothermic process, meaning it is endothermic and thus using heat to do so).

If a reaction is endothermic (deltaH is positive), it means that energy is being used to go from product to reactant. So if you were to give an endothermic system more energy to use, it would do more of the reaction as a result. And assuming the temperature stays contained within the system, the temperature has no place to go, so the reverse (exothermic) reaction won't happen as frequently as the endothermic one does.

[Jessica Li 3H]

If a reaction is endothermic, then change in enthalpy would be positive. If temperature increases, then Kc would also increase because the reaction would favor products and K would go up. If temperature goes down, then the reaction would shift towards reactants and Kc would go down.
If a reaction is exothermic, then change in enthalpy would be negative. If temperature increases, then Kc would decrease because the reaction favors reactants that have a higher enthalpy. If temperature decreases, then Kc would increase because products would be favored.