Why does only Temp affect K?

DLee_1L
Posts: 103
Joined: Sat Aug 17, 2019 12:17 am

Why does only Temp affect K?

Can anyone explain to me why is temperature the only thing that can affect the equilibrium constant? I can kind of see why for Kp because of the PV/T balancing, but don't understand why temperature affects Kc?

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Joined: Fri Sep 28, 2018 12:28 am

Re: Why does only Temp affect K?

Kc is dependent on temperature. A change in T would change the value of Kc, and this value will scale with respect to what kind of reaction is occurring (endothermic/exothermic).

Jessica Li 4F
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Joined: Fri Aug 09, 2019 12:16 am

Re: Why does only Temp affect K?

For any given concentrations, the ratio will always be the same, regardless of what the concentrations are, so they don't change the value of K. However, temperature affects K because changes in temperature shift the reaction toward a certain side. Think of temp. as a reactant or product in the reaction. If endothermic, it would look something like this:
Reactants + Temperature -> Products
If you increase the temperature, the reaction will shift toward the products in equilibrium, and hence Kc would be have to be changed.

Tyler Angtuaco 1G
Posts: 130
Joined: Wed Sep 11, 2019 12:16 am

Re: Why does only Temp affect K?

Just a speculation, but I would assume temperature affects the rate at which a reaction occurs, causing the equilibrium values of products and reactants to be different. This is because the temperature affects the viability of a reaction in the first place and thus the amount of products formed/reactants used.

William Francis 2E
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Joined: Wed Sep 18, 2019 12:20 am

Re: Why does only Temp affect K?

Temperature affects Kc because the forward reaction is either exothermic or endothermic. If the forward reaction is endothermic, then the Kc value will be larger when the temperature is higher since the forward reaction will absorb the added heat and produce a greater proportion of products to reactants than at a lower temperature. Similarly, the Kc value will decrease as temperature increases if the forward reaction is exothermic and the reverse reaction is endothermic.

lauraxie2e
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Joined: Fri Aug 09, 2019 12:17 am

Re: Why does only Temp affect K?

Temperature is combined with the reactants to form the products so when you increase the temperature more reactants are formed changing K

Posts: 102
Joined: Tue Oct 02, 2018 12:16 am

Re: Why does only Temp affect K?

Temperature can alter the stability of the molecules in the reaction. Hence, by changing the temperature, the products or reactants may become more/less stable at different temperatures. With this information, the reaction my shift to the left or right, altering our K.

Celine 1F
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Re: Why does only Temp affect K?

If the temperature changes, the reaction shifts to one side in equilibrium, changing K

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Re: Why does only Temp affect K?

William Francis 2E wrote:Temperature affects Kc because the forward reaction is either exothermic or endothermic. If the forward reaction is endothermic, then the Kc value will be larger when the temperature is higher since the forward reaction will absorb the added heat and produce a greater proportion of products to reactants than at a lower temperature. Similarly, the Kc value will decrease as temperature increases if the forward reaction is exothermic and the reverse reaction is endothermic.

How do we know if the forward reaction is exothermic or endothermic?

Posts: 81
Joined: Fri Sep 28, 2018 12:28 am

Re: Why does only Temp affect K?

William Francis 2E wrote:Temperature affects Kc because the forward reaction is either exothermic or endothermic. If the forward reaction is endothermic, then the Kc value will be larger when the temperature is higher since the forward reaction will absorb the added heat and produce a greater proportion of products to reactants than at a lower temperature. Similarly, the Kc value will decrease as temperature increases if the forward reaction is exothermic and the reverse reaction is endothermic.

How do we know if the forward reaction is exothermic or endothermic?

I believe that this would be a matter of checking the change in enthalpy ($\Delta H$). Positive would be endothermic, negative would be exothermic.

DLee_1L
Posts: 103
Joined: Sat Aug 17, 2019 12:17 am

Re: Why does only Temp affect K?

Yeah, you can't really tell if a reaction is exo or endothermic just by looking at the equilibrium constant. Enthalpy is the best way to see if a reaction is exothermic or endothermic because it is the measurement of how much heat is transferred. If enthalpy is negative, heat is leaving the system thus exothermic. If heat is entering the system, enthalpy is positive, thus endothermic.