Can someone help me with Kc Please?

OP

wait so let say A+B → 3C. A B and C are all gases
initially in GCSE we say if pressure increase then the position of equilibrium shifts to the left since there are less moles.
Now in A level, do we say that position of equilibrium shifts to the left to restore the value of Kc to reach equilibrium once again, right? Surely that would mean that at the instant of increasing the pressure, the position of equilibrium lies well on the right so that it needs to shift back to left to restore equilibrium?

Also since Kc is constant why would change in temperature change Kc?

Original post by weakweakling

Because Kc is a constant. It shows that when you disturb a condition in a system that is at equilibrium, the system will oppose that change so that equilibrium can be established again. So for example if you increased pressure, the system will favour the side of the reaction where there are fewer gas molecules, so as to reduce the pressure again. This maintains equilibrium, which is why Kc is constant.

Hope this makes sense!

(edited 5 years ago)

Reply 3

HateOCR

22

Only temperature affects Kc. If you disturb the equilibrium, it will oppose the disturbance and shift to the side where there is less disturbance. This effectively means that the concentration of reactants and products remains the same so Kc does not change.

Reply 4

the reason why we say kc isnt effected by pressure is because a pressure has to be maintained in order to disrupt the eq so, in a system if pressure is changed the eq is temporarily not = to kc

Original post by Iconic_panda

In GCSE we learnt about how change in concentration and pressure will change the position of equilibrium but how come it doesn't change Kc since Kc can measure the position of equilibrium

(edited 5 years ago)

Reply 5

OP

sorry lemme check out your new quote now.

Original post by nj1234

the reason why we say kc isnt effected by temp is because a temperature has to be maintained in order to disrupt the eq so, in a system if temp is changed the eq is temporarily not = to kc

(edited 5 years ago)

Reply 6

Original post by Iconic_panda

wait lemme reread sorry

i meant preassure my bad ^^

Reply 7

OP

Wait so to summarise.
so when pressure is increased the equilibrium is distorted. kc stays the same
Therefore the position of equilibrium needs to shift to restore Kc? (e.g left)
Does that therefore imply that at the instant that the pressure is changed (when equilibrium is distorted) the position lies on the right so that it needed to shift to left to restore Kc?

Original post by nj1234

the reason why we say kc isnt effected by pressure is because a pressure has to be maintained in order to disrupt the eq so, in a system if pressure is changed the eq is temporarily not = to kc

Reply 8

OP

it's alright bro I get what you mean

Original post by nj1234

i meant preassure my bad ^^

Reply 9

OP

Even then, why does temperature affect Kc since temperature surely disrupts the equilibrium too?

Reply 10

Original post by Iconic_panda

Wait so to summarise.
so when pressure is increased the equilibrium is distorted. kc stays the same
Therefore the position of equilibrium needs to shift to restore Kc? (e.g left)
Does that therefore imply that at the instant that the pressure is changed (when equilibrium is distorted) the position lies on the right so that it needed to shift to left to restore Kc?

kc is a fixed constant, therefore as soon as the preassure is no longer maintained, the system will revert back to the initial eq because the pressure is nolonger being exerted on the system, therefore kc doesnt change is just that its 'distorted' as you put it

Reply 11

OP

I think I get it now. So the 'revert back' is the same as 'shift the equilibrium to left to restore Kc'?

Original post by nj1234

kc is a fixed constant, therefore as soon as the preassure is no longer maintained, the system will revert back to the initial eq because the pressure is nolonger being exerted on the system, therefore kc doesnt change is just that its 'distorted' as you put it

Reply 12

Original post by Iconic_panda

Even then, why does temperature affect Kc since temperature surely disrupts the equilibrium too?

this ones quite simple. for pressures we use kp not kc as kp works for gaseous systems. we can change the temp and therefore KE of both gases AND liquids. however you cannnot change the pressure of a liquid! therefore change in pressure is said to have no real effect
pm me if this still doesnt make sense

Reply 13

pjrodarte339

12

If you put an 'f' inbetween the 'k' and the 'c', you get 'kfc'. Hope that helped.

Reply 14

Original post by pjrodarte339

If you put an 'f' inbetween the 'k' and the 'c', you get 'kfc'. Hope that helped.

teach me please :smile:

Reply 15

pjrodarte339

12

Original post by nj1234

teach me please :smile:

My godly teachings cannot be understood by mere mortals.

Reply 16

Original post by pjrodarte339

My godly teachings cannot be understood by mere mortals.

mere mortal i am not! the infamous elixer ebbs and flows through my veins... a'las you say you can'th teac'th me

Reply 17

pjrodarte339

12

Original post by nj1234

mere mortal i am not! the infamous elixer ebbs and flows through my veins... a'las you say you can'th teac'th me

You show great potential, young one. I may reconsider my previous post...

Reply 18

OP