Direction of a non-equilibrium reaction

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Carolina Gomez 2G
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Direction of a non-equilibrium reaction

Postby Carolina Gomez 2G » Thu Jan 07, 2021 2:42 pm

Why is it that when Q is greater than K, the reverse reaction is favored and when Q is less than K the forward reaction is favored?

ChihWei Chen 2C
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Re: Direction of a non-equilibrium reaction

Postby ChihWei Chen 2C » Thu Jan 07, 2021 2:49 pm

Correct me if I'm wrong but this is the way that I understand it: When Q is greater than K, there is too much product since Q = concentration of product over reactant. In order for it to reach equilibrium, Q has to equal to K so more reactants have to be made to make Q smaller. Hence the reverse reaction is favored.
Same thing can be said for when Q is smaller than K: too many reactants made so more products must be produced to make Q larger and become K. So the forward reaction is favored.

Courtney Situ 2B
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Re: Direction of a non-equilibrium reaction

Postby Courtney Situ 2B » Thu Jan 07, 2021 2:51 pm

Hi there!

Q and K both have the same formula ([products]/[reactants]), but K specifically describes when the reaction is in equilibrium and Q can be used to describe the reaction whenever. K is also a set value (as long as temperature does not change), but Q can change. Reactions want to approach equilibrium, so Q will try to become K (the value Q should be at equilibrium).

When Q is greater than K, that means the ratio of [products]/[reactants] in the reaction is greater than the ratio would be at equilibrium. To decrease this Q ratio (so that it matches K again), the reaction will shift left, decreasing the [products] and increasing the [reactants]. The reverse reaction is favored.

When Q is less than K, that means the ratio of [products]/[reactants] in the reaction is less than the ratio would be at equilibrium. To increase this Q ratio (so that it matches K again), the reaction will shift right, increasing the [products] and decreasing the [reactants]. The forward reaction is favored.

Hope that helps!

Marisa Gaitan 2D
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Re: Direction of a non-equilibrium reaction

Postby Marisa Gaitan 2D » Thu Jan 07, 2021 2:53 pm

When Q is less than K, the forward reaction, product formation, is favored because Q is smaller as a result of a larger denominator (reactants). In order to reach equilibrium, more products must be formed. Same goes the other way. When Q is greater than K, the reverse reaction is favored because there must have been more product formation (numerator) to achieve a Q value larger than K. The reverse reaction would favor the reactants and thus would bring the Q value down to K. This concept is definitely hard to explain in words, but I hope this clears some stuff up.

Sukhkiran Kaur 3I
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Re: Direction of a non-equilibrium reaction

Postby Sukhkiran Kaur 3I » Thu Jan 07, 2021 4:04 pm

I think it's dependent on the product/reactant quantity based on the formula.

Jason_Glass_2L
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Re: Direction of a non-equilibrium reaction

Postby Jason_Glass_2L » Thu Jan 07, 2021 5:35 pm

To add on, a good way to visualize this is like a see-saw, if Q>K, the amount of products would be greater than at equilibrium because =Products/reactants. We want the the amount on each sides to reach equilibrium, so we would favor the left (reactants) side to do so.

Alexandra Ahlschlager 1L
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Re: Direction of a non-equilibrium reaction

Postby Alexandra Ahlschlager 1L » Thu Jan 07, 2021 5:50 pm

If Q is less than K, this means that the value of the denominator (reactants) is too big and the numerator (products) is too small. In other words, there are too many reactants in the reaction compared to how much there needs to be in order for the reaction to be at equilibrium. Therefore, in order to shift towards equilibrium it will need to decrease reactants by forming more products, meaning the reaction will proceed to the right. You can use this same reasoning for when Q is greater than K as well. Hope this helps a little!

Kamille Kibria 2A
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Re: Direction of a non-equilibrium reaction

Postby Kamille Kibria 2A » Fri Jan 08, 2021 1:58 am

when Q<K it means that the concentration of products are lower than the reactants compared to equilibrium, so the forward reaction is favored.
when Q>K it means that the concentration of reactants are lower than the products compared to at equilibrium, so the reverse reaction is favored.
the way i visualize these types of problems is to think of the system as compensatory and that the goal is to reach equilibrium. what also helps me visualize is to understand how the numerator and denominator compare when given Q or K to give you the relative concentrations of reactant and product.

rhettfarmer-3H
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Re: Direction of a non-equilibrium reaction

Postby rhettfarmer-3H » Sun Jan 10, 2021 6:52 pm

I learned this in LS7A but it has to do with the amount of product and reactants and le chalifer principal. So if Q is really big we have a lot of product. We know from le chalifer that the reaction wants to be at equilibrium. So, it must adapt and produce the reverse so it returns to its stable state. Likewise for a low Q which means high reactants which favors the production of products because it wants to get that stable K ratio.

MichaelRaad_1F
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Re: Direction of a non-equilibrium reaction

Postby MichaelRaad_1F » Sun Jan 10, 2021 7:11 pm

When Q is less than K it means that there are more reactants than products and therefore the forward reaction is favored due to the excess of reactants in the chemical reaction.

James Fu 2F
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Re: Direction of a non-equilibrium reaction

Postby James Fu 2F » Sun Jan 10, 2021 7:12 pm

Q is the same as the equation we use to determine the equilibrium constant, but it lets us determine which way the reaction will go at any given time. P (the concentration of products) is in the numerator. Thus, we must have a lot of product if Q is larger than K. When we have a large amount of product, the products will decompose into reactants and thus the reverse reaction is favored.

On the other hand, if Q is smaller than K reactants tend to form products since Q wants to head towards K and in order for this to happen the amount of product would have to increase.

Karen Zheng_2K
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Re: Direction of a non-equilibrium reaction

Postby Karen Zheng_2K » Sun Jan 10, 2021 7:21 pm

This is due to the fact that when Q is less than K there are more reactants present which would automatically make the forward reaction (--->) more favorable!


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