Reaction Quotient(Q) vs. Equilibrium Constant(K)


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Yeonjoo Kim 2B
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Reaction Quotient(Q) vs. Equilibrium Constant(K)

Postby Yeonjoo Kim 2B » Thu Jan 07, 2021 2:55 pm

Hello, can anyone explain the differences between Q and K?

ChihWei Chen 2C
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Re: Reaction Quotient(Q) vs. Equilibrium Constant(K)

Postby ChihWei Chen 2C » Thu Jan 07, 2021 3:02 pm

Q describes the relation between the product and reactant concentrations at any point in the reaction, and K describes the relation between the product and reactant concentrations in equilibrium.
So only concentrations at equilibrium can be used to plug into K, although it has the same equation as Q.

Kailani_Dial_2K
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Re: Reaction Quotient(Q) vs. Equilibrium Constant(K)

Postby Kailani_Dial_2K » Thu Jan 07, 2021 3:03 pm

Hello, so K is the equilibrium constant. This means this is the value when the rate of the forward and reverse reaction are equal. Q is basically a preliminary value before K. Q provides you the rate at which the forward and reverse reactions are proceeding but they are not yet at equilibrium. You would know if you were finding a Q value becuase if you took the concentration of the products over the reactants at lets say 1 o clock and then came back 3 hours later at 4 o clock and computed a different value, then you know that the reaction was not at equilibrium since the K value does not change once equilibroum is hit.

I guess the too long to read version would be that Q is a preliminary value describing the ratio of products to reactants before equilibrium is achieved.

Courtney Situ 2B
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Re: Reaction Quotient(Q) vs. Equilibrium Constant(K)

Postby Courtney Situ 2B » Thu Jan 07, 2021 3:04 pm

Hi there!

Reaction quotient (Q) and equilibrium constant (K) have the same overall formula: [products]/[reactants]. However, the equilibrium constant specifically tells us what the ratio should be when the reaction hits equilibrium, and it only changes if temperature changes. The Q tells us the ratio at any given moment, and it will change accordingly with the environment (temperature changes, pressure changes for gases, amount of reactants/products, etc.)

I think the most important thing to remember though is that K doesn't change unless temperature changes. Also, reactions naturally try to change their Q value to equal the equilibrium constant (they try to reach equilibrium).

Hope that helps!

Marisa Gaitan 2D
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Re: Reaction Quotient(Q) vs. Equilibrium Constant(K)

Postby Marisa Gaitan 2D » Thu Jan 07, 2021 3:06 pm

For reactions not at equilibrium, the reaction quotient Q tells us whether the forward or reverse reaction will be favored in order to reach equilibrium. For instance, if Q>K, the reverse reaction is favored whereas if Q<K, the forward reaction is favored. And when the reaction is at equilibrium, Q is equal to K. Q basically tells us how the reaction will "behave" until it reaches the Q=K equilibrium state.

Jordan Tatang 3L
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Re: Reaction Quotient(Q) vs. Equilibrium Constant(K)

Postby Jordan Tatang 3L » Thu Jan 07, 2021 4:35 pm

just reiterating what everyone else already said Q is at any point in the reaction and K is when the reaction is known to be at equilibrium

Jordi M 2I
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Re: Reaction Quotient(Q) vs. Equilibrium Constant(K)

Postby Jordi M 2I » Thu Jan 07, 2021 4:39 pm

One important thing to note is that many will refer to an equilibrium as shifted or leaning to the right or left. This does not mean the reaction is not at equilibrium, this means the forward reaction either favors products or reactants more. A Q value on the other hand can physically lay right or left of an equilibrium. If Q > K, the quotient has too much product (too far right) and will proceed leftward. If Q < K, the quotient has too little product and will proceed right.

Nayra Gharpetian 3F
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Re: Reaction Quotient(Q) vs. Equilibrium Constant(K)

Postby Nayra Gharpetian 3F » Thu Jan 07, 2021 4:53 pm

Q is at any point in the reaction but K is at equilibrium. comparing Q and K can tell you that the reaction is at equilibrium, or whether the reaction will shift to the right or the left to reach equilibrium

Sabrina Galvan 3J
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Re: Reaction Quotient(Q) vs. Equilibrium Constant(K)

Postby Sabrina Galvan 3J » Thu Jan 07, 2021 6:43 pm

The reaction quotient is used to calculate the ratio of products to reactants at any point during its reaction, and its most important purpose is how it compares to K, the fixed ratio of products and reactants at equilibrium. If Q = K, then the reaction is at equilibrium, however if it does not equal K, then it is not. When Q is larger than K, that means that there are more products in the reaction currently than the amount of products that are present when it is in equilibrium, so the reverse reaction will be favored to decrease the value of Q because it decreases the amount of products and increases the amount of reactants. When Q is less than K, that means there are less products than when the reaction is in equilibrium, so the forward reaction is favored to increase Q through the process of creating more products and less reactants.

Sai Ramadas 1J
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Re: Reaction Quotient(Q) vs. Equilibrium Constant(K)

Postby Sai Ramadas 1J » Fri Jan 08, 2021 12:59 pm

Basically, Q is a test value of K. If you calculate the ratio of the concentrations of products to reactants (the same way you normally would for K), and it is not equal to K, we call it Q. If Q<K, then we know the reaction will favor the forward reaction (R->P). If Q>K, then we know the reaction will favor the reverse reaction (P->R).


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