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### Difference between K and Q?

Posted: Fri Jan 17, 2020 11:19 pm
The reaction quotient (Q) formula looks very similar to the formula used for the equilibrium constant, K so what is their difference? Is it just that K has to be at equilibrium or is there other differences between them?

### Re: Difference between K and Q?

Posted: Sat Jan 18, 2020 12:33 am
Q and K have the exact same formula. Q can be any value depending on the state of the reaction. K is Q when the reaction reached equilibrium.

### Re: Difference between K and Q?

Posted: Sat Jan 18, 2020 1:47 am
Yeah, K is at equilibrium while Q is at any stage of the reaction.

### Re: Difference between K and Q?

Posted: Sat Jan 18, 2020 10:24 am
K represents the concentrations at equilibrium whereas Q represents concentrations not at equilibrium

### Re: Difference between K and Q?

Posted: Sat Jan 18, 2020 10:55 am
Q and K are both measured by the ratio of products over reactants, but K represents that ratio at equilibrium while Q can represent that ratio at any point in the reaction.

### Re: Difference between K and Q?

Posted: Sat Jan 18, 2020 11:31 am
K is a fixed value for the reaction, while Q varies if the reaction is/is not yet at equilibrium and we can compare the two values to determine if the reaction is at equilibrium or not.

### Re: Difference between K and Q?

Posted: Sat Jan 18, 2020 11:44 am
Is the formula always the same for Q and K? I know whether we use Q or K depends on the equilibrium status of the reaction, but we find the values the exact same way otherwise?

### Re: Difference between K and Q?

Posted: Sat Jan 18, 2020 1:36 pm
The formula's the same and you find it in the same way, but you use current concentrations/pressures for Q and equilibrium concentrations/pressures for K.

### Re: Difference between K and Q?

Posted: Sat Jan 18, 2020 4:22 pm
K is the equilibrium constant and can only be solved for when the concentrations of reactants and products at equilibrium are known. Q is the reaction quotient and can be solved at any point in the reaction, regardless if it is in equilibrium. If Q<K then the reaction moves forward and favors the products. If Q>K then the reaction moves reverse and favors the reactants.

### Re: Difference between K and Q?

Posted: Sun Jan 19, 2020 12:30 am
Q is calculated the same was as K. However, K is the equilibrium constant while Q is the reaction quotient at any time during the reaction. You compare Q to K in order to find out whether the reaction is at equilibrium or not. When Q<K, the forward reaction is favored since the concentration of reactants is higher than the concentration of products. When Q>K, the reverse reaction is favored. If Q=K, the reaction is at equilibrium.

### Re: Difference between K and Q?

Posted: Sun Jan 19, 2020 1:25 pm
They look very similar because the only difference between the two constants is when you should use them. You use K when the reaction is at equilibrium, and you use Q at any stage of the reaction. You can compare the two constants to determine which way the reaction is shifting.

### Re: Difference between K and Q?

Posted: Sun Jan 19, 2020 2:25 pm
Q and K are actually calculated using the same formula with products over reactants. The difference between the two lies in when they apply. K ONLY applies to when a reaction has reached equilibrium. On the other hand, Q can represent any time during a reaction. Using Q, you an determine if the reaction is at equilibrium (K=Q) or what direction the reaction is moving in depending on if K>Q or K<Q.