Changing Kc  [ENDORSED]

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Suraj Doshi 2G
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Changing Kc

Postby Suraj Doshi 2G » Thu Jan 09, 2020 9:44 am

Why does only a change in temperature change Kc whereas a change in pressure and/or volume does not?

Jialun Chen 4F
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Re: Changing Kc

Postby Jialun Chen 4F » Thu Jan 09, 2020 9:54 am

I think the equilibrium constant Kc does not change for the same reaction under the same temperature no matter what masses of reactants one uses.

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Re: Changing Kc

Postby VPatankar_2L » Thu Jan 09, 2020 9:56 am

A change in pressure is brought about by a change in volume. A change in pressure can cause the reaction to shift to the left or to the right based on the number of moles of products and reactants. But this shift occurs to restore the value of the equilibrium constant.

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Re: Changing Kc

Postby 105335337 » Thu Jan 09, 2020 10:02 am

A change in pressure & or volume results in a change in the opposite. These just cause the reaction to go forward or backward and then eventually re-reach equilibrium. Temperature causes the molecules to speed up while nothing else is changing, causing more of them to hit each other.

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Re: Changing Kc  [ENDORSED]

Postby Chem_Mod » Thu Jan 09, 2020 10:04 am

I will discuss this in class in both the equilibrium and kinetics sections.

Changing the volume in a gas phase reaction changes concentrations, and changing concentrations does not change K.
I will discuss this in detail this Friday and Monday in class.

The activation barrier is different in the forward and reverse reactions, and changing the temperature permanently changes the number of collisions with enough energy to overcome the activation energy. The key point here is the temperature effect is non-linear (see Arrhenius equation). I'll discuss this when we get to kinetics.

Good question.

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