### K vs Q

Posted:

**Thu Jan 10, 2019 7:23 pm**What's the difference between the formula for the equilibrium constant K and the formula for the reaction quotient Q?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=50&t=39629

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Posted: **Thu Jan 10, 2019 7:23 pm**

What's the difference between the formula for the equilibrium constant K and the formula for the reaction quotient Q?

Posted: **Thu Jan 10, 2019 7:48 pm**

Q changes as a reaction occurs, and K is when said reaction reaches equilibrium. If the reaction does't reach equilibrium, you can't use K, only Q

Posted: **Thu Jan 10, 2019 7:49 pm**

The formula is the same. What's different between the two is the concept behind it. The equilibrium constant K is the ratio at equilibrium; it describes a reaction that is at equilibrium. On the other hand, the reaction quotient pertains to the ratio at any given time of the reaction.

This might elucidate the topic further: viewtopic.php?f=50&t=24065

This might elucidate the topic further: viewtopic.php?f=50&t=24065

Posted: **Thu Jan 10, 2019 7:50 pm**

The formula for K and Q is the same; the difference is that the numbers you plug in for K must be the equilibrium partial pressures or concentrations while for Q you can plug in the partial pressures or concentrations at any point in the reaction, not just at equilibrium.

Posted: **Thu Jan 10, 2019 8:47 pm**

The formula to find K and Q are the same. However, K is the ratio of at equilibrium and therefore includes the values of the reaction at equilibrium. Meanwhile, Q is the reaction quotient and is the ratio at any given time in the reaction.

Posted: **Sun Jan 13, 2019 11:39 am**

The formula is the same, but K is the ratio at equilibrium, whereas Q is the reaction quotient. The numbers you plug in decide whether you're using K or Q.

Posted: **Sun Jan 13, 2019 8:43 pm**

So can there be only one value for K but multiple values for Q as the reaction progresses?

Posted: **Sun Jan 13, 2019 8:49 pm**

The partial pressures and concentrations do not have to be at equilibrium for Q but they do for K. Other than that, it's the same equation.