The Difference between Q and Kc [ENDORSED]

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VivianaHF2L
Posts: 29
Joined: Fri Sep 28, 2018 12:20 am

The Difference between Q and Kc

What is the difference between the two, in terms of comparing them if they have the same formula? What does the comparison entail?

whitney_2C
Posts: 74
Joined: Fri Sep 28, 2018 12:28 am

Re: The Difference between Q and Kc

Q is different from Kc because Kc indicates the ratio of products to reactants at equilibrium while Q indicates the ratio of products to reactants at any time during the reaction (such as when it has not yet reached equilibrium) we can then use Q to figure out which direction a reaction is sitting toward by comparing it to the reaction's Kc value.

Ariel Cheng 2I
Posts: 67
Joined: Fri Sep 28, 2018 12:29 am

Re: The Difference between Q and Kc

As said above, Q has the same formula as Kc but can be calculated at anytime, not just when a reaction is at equilibrium. To explain the comparison a little more, when Q < Kc, a forward reaction will be favored. This is because Q is calculated as [products] / [reactants]. If Q is smaller than Kc, we need to increase the concentration of products in order to bring it up to match Kc (equilibrium). If Q > Kc, the opposite will be true. If Q = Kc, then the reaction has already reached equilibrium.

Sophie Roberts 1E
Posts: 61
Joined: Fri Sep 28, 2018 12:17 am

Re: The Difference between Q and Kc

We use Q to determine which way the reaction must proceed to reach equilibrium which can also help us in settling up our ICE boxes.

charlotte_jacobs_4I
Posts: 63
Joined: Fri Sep 28, 2018 12:29 am

Re: The Difference between Q and Kc

Q is the same equation as K, but Q is calculated at anytime during the reaction and compared to K. If K and Q match then the system is at equilibrium. If Q<K it moves towards the products, if Q>K it moves towards the reactants.

EllaBerry
Posts: 68
Joined: Fri Sep 28, 2018 12:29 am

Re: The Difference between Q and Kc

Q and K are both calculated in the same way. However, they are different in that Q can be calculated at any time during the reaction, while K is the value only at equilibrium. Therefore you can use Q in comparison to K to determine which way a reaction is "shifted" towards. If Q is less than K, the reactions lies to the right, or favors the products.

Katie_Duong_1D
Posts: 69
Joined: Fri Sep 28, 2018 12:27 am

Re: The Difference between Q and Kc

Q is the reaction quotient. K is the equilibrium constant. Q can be calculated at anytime during the reaction, while k is only at equilibrium. If Q<K, then the reaction shifts right to reach equilibrium. If Q>K, then the reaction shifts left to reach equilibrium.

Posts: 64
Joined: Fri Sep 28, 2018 12:26 am

Re: The Difference between Q and Kc  [ENDORSED]

Q and K are calculated the same way (products/reactants), but Q can be measured at any point of the reaction and K is only measured at equilibrium. If Q < K then the forward reaction is favored. If Q > K then the reverse reaction is favored.

Anna O 2C
Posts: 98
Joined: Fri Sep 28, 2018 12:19 am

Re: The Difference between Q and Kc

Kc is the value of Q taken only at equilibrium while Q is the same ratio but taken at anytime during the reaction, not specifically at equilibrium.

105085381
Posts: 44
Joined: Fri Sep 28, 2018 12:15 am

Re: The Difference between Q and Kc

Both Q and K are calculated using the same equations - Q can calculate a particular point of the reaction / K calculates the reaction at equilibrium!

Brian Hom 2F
Posts: 60
Joined: Fri Sep 28, 2018 12:24 am

Re: The Difference between Q and Kc

Q and Kc are both constants used to look at a reaction. Q deals with the the reaction not at equilibrium and it can tell what direction the reaction will proceed as it moves toward equilibrium. When Q>K, reaction favors reverse. When Q<K, reactions favors forward. Kc is the equilibrium constant and this value tells you the ratio between products to reactants.

PranitKumaran1F
Posts: 30
Joined: Thu Nov 08, 2018 12:17 am

Re: The Difference between Q and Kc

K is the ratio of the products and reactants when the reaction is at equilibrium only, while Q is the ratio of the products and the reactants at any given point in the reaction.

jocelyntzeng
Posts: 59
Joined: Fri Sep 28, 2018 12:18 am

Re: The Difference between Q and Kc

q is the ratio of products and reactants at that moment whereas Kc is the ratio at equilibrium

905289082
Posts: 61
Joined: Fri Aug 09, 2019 12:16 am

Re: The Difference between Q and Kc

how does Kc take into account the values of partial pressure?

Juana Abana 1G
Posts: 55
Joined: Wed Sep 18, 2019 12:15 am

Re: The Difference between Q and Kc

Q and K are calculated using the same equation however, K calculates the reaction at equilibrium meanwhile Q can calculate a particular point in a reaction.

lauraxie2e
Posts: 66
Joined: Fri Aug 09, 2019 12:17 am

Re: The Difference between Q and Kc

Kc is only at equilibrium, while Q is at any time of the reaction

Robert Tran 1B
Posts: 70
Joined: Thu Jul 11, 2019 12:15 am

Re: The Difference between Q and Kc

Kc is calculated when the reaction is at equilibrium. On the other hand, Q is calculated when the reaction is at any other state.

Jaci Glassick 2G
Posts: 63
Joined: Sat Jul 20, 2019 12:16 am

Re: The Difference between Q and Kc

Kc occurs when the reaction is at equilibrium. Q is used at any other time during the reaction.

Daniel Chen 2L
Posts: 60
Joined: Fri Aug 30, 2019 12:15 am

Re: The Difference between Q and Kc

If you later find that you're wondering about the difference between Q and Kp (pressure, rather than Kc, which is concentration), then you can just come back here because it's pretty much similar, I think.