K and Q


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Shuyi Yu 1B
Posts: 60
Joined: Fri Sep 28, 2018 12:16 am

K and Q

Postby Shuyi Yu 1B » Sat Jan 12, 2019 6:15 pm

If Q and K both have the same formula why are they not equal to each other?

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

Re: K and Q

Postby Ariel Cheng 2I » Sat Jan 12, 2019 6:23 pm

They have the same formula but don't equal each other because K is calculated using molarities at equilibrium but Q is calculated using molarities at any point in time during the reaction. We can then use Q and compare it to K to see at where the reaction is at. If Q<K, then a forward reaction is favored because Q and K are products/reactants and we need more products to increase the value of Q. The opposite is true if Q>K.

Karina Jiayu Xu 4E
Posts: 58
Joined: Fri Sep 28, 2018 12:29 am

Re: K and Q

Postby Karina Jiayu Xu 4E » Sat Jan 12, 2019 6:47 pm

K is used for the exact equilibrium state and Q is used for anytime during the reaction. When they are not exactly the same then the current reaction is leaning one direction or the other.

SydBenedict2H
Posts: 60
Joined: Wed Nov 08, 2017 3:00 am

Re: K and Q

Postby SydBenedict2H » Sat Jan 12, 2019 9:51 pm

K calculates the equilibrium constant (either with partial pressure P or concentration n/v) whereas Q can be use anytime and is useful in its comparison to a K value. Whether it is greater than or less than the reactions K value, dictates which direction the reaction is going and if there are more products or reactants.

Ethan Yi 1K
Posts: 62
Joined: Fri Sep 28, 2018 12:28 am

Re: K and Q

Postby Ethan Yi 1K » Sat Jan 12, 2019 11:36 pm

K is the [products]/[reactants] at equilibrium. Q can be used anytime during the reaction. For instance, at the very start of the reaction, there may be a lot more reactants than products, and at this point, [products]/[reactants] would be Q, not K bc the reaction is not at equilibrium yet.

Harshita Talkad 4L
Posts: 60
Joined: Fri Sep 28, 2018 12:16 am

Re: K and Q

Postby Harshita Talkad 4L » Sat Jan 12, 2019 11:57 pm

K is calculated with the concentrations of the reactants and products when the reaction is at equilibrium, which means K will always be constant as long as it is the same reaction at the same temperature. Q can be calculated at any point in the reaction, so there will be different concentrations of reactants and products at each point in time, so Q is different depending on when in the reaction it is calculated. Q is compared to K to determine if the reaction is at equilibrium at that point in time.

Alyssa Wilson 2A
Posts: 65
Joined: Fri Sep 28, 2018 12:18 am

Re: K and Q

Postby Alyssa Wilson 2A » Sun Jan 13, 2019 9:09 am

I agree with the above statements, and Q is known as the reaction coefficient, which is similar to k, but it can be used in any stage of the reaction, where k is used and solids and liquids do not contribute into k. K is the equilibrium constant and the rate of the forward reaction will equal the rate of the reverse reaction.

404982241
Posts: 47
Joined: Fri Sep 28, 2018 12:17 am

Re: K and Q

Postby 404982241 » Sun Jan 13, 2019 8:36 pm

K is the equilibrium constant. Its value is only true once the reaction has reached equilibrium. Q can be calculated any time during the reaction. Regardless of the amount of products and reactants used, K will always be the same.


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