Q and K on and reactant/product concentrations

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Lucy Wang 2J
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Q and K on and reactant/product concentrations

Postby Lucy Wang 2J » Sun Jan 10, 2021 11:31 pm

during lecture 2, Professor Lavelle said that if Q<K during a reaction, then [R]>[P] and the forward reaction is favored. however, isn't it possible for Q<K but for [P] to be greater than [R]?

Ellison Gonzales 1H
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Re: Q and K on and reactant/product concentrations

Postby Ellison Gonzales 1H » Sun Jan 10, 2021 11:35 pm

Hi Lucy! My understanding is that if [P] is greater than [R], then that means products are added to the equilibrium mixture and so Q temporarily rises above K since products appear in the numerator. So I think Q would no longer be less than K. Section 5J in the book talks about this a bit, you may be able to find an answer there too :)

Kyle Walsh 2J
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Re: Q and K on and reactant/product concentrations

Postby Kyle Walsh 2J » Sun Jan 10, 2021 11:37 pm

Fancy seeing you here. I believe that it's not possible for Q to be smaller than K while [P] is greater than [R], because Q is equal to [P]/[R]. Meaning that when [P] is greater than [R], Q is going to be some number over 1, whereas K would be 1, as [P]=[Q] for K.

Ellison Gonzales 1H
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Re: Q and K on and reactant/product concentrations

Postby Ellison Gonzales 1H » Sun Jan 10, 2021 11:38 pm

Could someone list what terms are used when talking about Q? I get a bit confused on which terms are used for K or Q

Adrienne Chan 1G
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Re: Q and K on and reactant/product concentrations

Postby Adrienne Chan 1G » Sun Jan 10, 2021 11:38 pm

In the second scenario you mention, for [P] being greater than [R], this would mean that the condition Q<K is no longer true, and the reverse reaction would be favored. Hope this helps!

Lakshmi Davuluri 1E
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Re: Q and K on and reactant/product concentrations

Postby Lakshmi Davuluri 1E » Thu Jan 14, 2021 10:15 pm

Ellison Gonzales 1H wrote:Could someone list what terms are used when talking about Q? I get a bit confused on which terms are used for K or Q

K is the equilibrium constant, while Q is the reaction quotient.

Mackenzie Stockton 2H
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Re: Q and K on and reactant/product concentrations

Postby Mackenzie Stockton 2H » Fri Jan 15, 2021 11:29 am

Q = [P] / [R], so if Q<K, there is no way that the reactant concentration could be greater than the products and Q be <K.

Olivia Monroy 1A
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Re: Q and K on and reactant/product concentrations

Postby Olivia Monroy 1A » Fri Jan 15, 2021 11:37 am

Q=[P]/[R], K=[P]/[R] so if Q<K this has to mean there was an increase in reactant from equilibrium concentration, the reactant concentration has to be greater than the product concentration, meaning the forward reaction is favored as Lavelle said. K=1 when [P]=[R] so if [P] is greater than [R] it is no longer true Q<K.

Samudrala_Vaishnavi 3A
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Re: Q and K on and reactant/product concentrations

Postby Samudrala_Vaishnavi 3A » Fri Jan 15, 2021 5:11 pm

Actually, when Q<K it is always the case that the reaction is a forward reaction since more products are formed than reactants, so [P] is always greater than [R]. I don't get where you got the info that [R]> [P] when Q<K since [R] is decreasing. In the questions having to do with Le Chatelier's principle and the adding or removing of reactants and products, Q can decrease to be less than K if we were to either remove reactants or add a product which is kind of the same thing.


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