## Q vs. K

$E_{cell} = E_{cell}^{\circ}-\frac{RT}{nF}\ln Q$

Hailey Johnson
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Joined: Wed Nov 16, 2016 3:04 am

### Q vs. K

What is the difference between Q and K and how do we know which one to use in a given problem?

Lourick Bustamante 1B
Posts: 50
Joined: Wed Nov 16, 2016 3:02 am

### Re: Q vs. K

Q is the the reaction quotient and K is the equilibrium constant. Both Q and K are calculated the same way (by using pressures or concentrations) but they are applied differently depending on the equation that you are using. Because they are calculated the same, it shouldn't make too much of a difference if you are calculating one or the other but the problem and equation should specify that for you.

Jessica_Singh_1J
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Joined: Fri Sep 29, 2017 7:03 am

### Re: Q vs. K

Q is the quotient calculated at non equilibrium conditions while K is the quotient calculated at equilibrium.

Sirajbir Sodhi 2K
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Joined: Sat Jul 22, 2017 3:00 am

### Re: Q vs. K

In much of what we do, Q is used when we want to calculate some sort of potential at non-standard conditions (Gibbs Free Energy, Nernst Equation). K is used in our calculations when we want to calculate the potential at standard conditions, usually.

diangelosoriano
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Joined: Fri Sep 29, 2017 7:07 am

### Re: Q vs. K

You must also be sure to make the distinction between capital K and lowercase k when we deal with kinetics (rate constant).

Alex Nechaev 1I
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Joined: Fri Sep 29, 2017 7:04 am

### Re: Q vs. K

K can be used calculate the final concentrations at equilibrium for a reaction using an ICE table and the natural progression of the reaction, from left to right or from right to left. Q expresses the relative ratio of products to reactants at a given instant.

Rachel Wang
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Joined: Fri Sep 29, 2017 7:04 am

### Re: Q vs. K

K is the equilibrium constant. Q is the constant when the rxn isn't at equilibrium and when compared to K can predict which way the rxn will proceed at that particular state. They are calculated the same way.

704887365
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Joined: Sat Jul 22, 2017 3:00 am

### Re: Q vs. K

Q is calculated under conditions at any given time while K is calculated while the reaction is at equilibrium.

Michael Downs 1L
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Joined: Thu Jul 13, 2017 3:00 am

### Re: Q vs. K

Q is used to compare to K for some reactions

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