Temperature and Kc

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Giselle Granda 3F
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Joined: Wed Sep 30, 2020 10:00 pm

Temperature and Kc

Postby Giselle Granda 3F » Sun Jan 17, 2021 10:39 pm

Can somebody explain how temperature affects the reactants and products in both an endothermic and exothermic reaction, as well as how it affects Kc?

Lucy Wang 2J
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Re: Temperature and Kc

Postby Lucy Wang 2J » Sun Jan 17, 2021 10:45 pm

when a reaction is endothermic, meaning energy is required for the reactants to go to products, if a reaction is heated this will favor the forward reaction/the formation of products so Kc will increase.

when a reaction is exothermic, meaning energy is released when the reactants go to products, if a reaction is heated this will favor the reverse reaction/the formation of reactants so Kc will decrease.

Meghan Krushena 2E
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Re: Temperature and Kc

Postby Meghan Krushena 2E » Sun Jan 17, 2021 10:46 pm

Sapling explains this really well:

A positive change in enthalpy indicates an endothermic reaction. For endothermic reactions, an increase in temperature causes an increase in K. The reaction quotient is not affected by the temperature change, since there is no change in concentrations.
A negative change in enthalpy indicates an exothermic reaction. For exothermic reactions, an increase in T causes a decrease in K.

Thomas Gimeno
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Joined: Wed Sep 30, 2020 9:49 pm

Re: Temperature and Kc

Postby Thomas Gimeno » Sun Jan 17, 2021 10:54 pm

Think of heat as just another product or reactant.

If the reaction is endothermic (delta H is positive) then heat would be a reactant: heat + ab --> a + b
If the reaction is exothermic (delta H is negative) then heat would be a product: ab--> a + b+ heat

Then if you think about adding more heat or taking it away, you can just think about it like adding a product or a reactant.
For example, if you add heat to the exothermic reactuon then it's like adding more of a product, this would shift the reaction to the left towards the reactants.

IreneGi2I
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Joined: Wed Sep 18, 2019 12:19 am

Re: Temperature and Kc

Postby IreneGi2I » Sun Jan 17, 2021 11:50 pm

Endothermic: Absorbs heat (requires heat) to form products
Exothermic: Releases heat (gives off heat) to form products

When heat is added,
1) Endothermic: Shift to right (more products form) --> [P] increases in [P]/[R] --> Therefore, Kc increases
2) Exothermic: Shift to left (more reactants form) --> [R] increases in [P]/[R] --> Therefore, Kc decreases

And vice versa for when it is cooled. Hope this helps!

Sam Wentzel 1F 14B
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Re: Temperature and Kc

Postby Sam Wentzel 1F 14B » Sun Jan 17, 2021 11:55 pm

It depends whether reaction is endothermic or exothermic.

If reaction is endothermic, and Temperature increases, then Kc will increase.
If Temperature decreases, then Kc will decrease.

If reaction is exothermic, and Temperature increases, then Kc will decrease.
If temperature decrease, Kc will increase.

Kc changes based on the changes in either the proportion of reactants or products induced by changes in temperature.


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