Page 1 of 1

### Calculating Q

Posted: Thu Jan 24, 2019 11:24 am
When do you calculate Q? I am having some trouble understanding why you would need this and when to use it.

### Re: Calculating Q

Posted: Thu Jan 24, 2019 12:24 pm
You calculate Q when you are not sure whether the reaction is at equilibrium. If you already know the reaction’s K value, you can use the same formula for K at any time, even when the reaction is not at equilibrium, and call the calculated value Q. Its value relative to K (whether it is less than K or greater than K) helps you to predict the future dynamics of the reaction. For example, if you calculate a Q that is less than K, you can infer that the reaction will then favor product formation over reactant formation to get closer to to the equilibrium state.

### Re: Calculating Q

Posted: Thu Jan 24, 2019 12:49 pm
Q uses the same equation as K, but it can be calculated at any point of the reaction, whereas K can only be calculated at equilibrium. You can then compare Q to K to find out where the reaction is relative to equilibrium and which way the reaction might favor.

### Re: Calculating Q

Posted: Thu Jan 24, 2019 1:26 pm
Both Q and K use the same equation during calculation. However, K is used at equilibrium while Q can be used at any point during a reaction. It is important understand the fact that Q can be changed due to changes in pressure and concentration but K does not. K shifts only when there is a change in temperature.

### Re: Calculating Q

Posted: Thu Jan 24, 2019 2:29 pm
You can calculate Q exactly how you would calculate K. Q = [products]/[reactants]. If Q<K, the reaction shifts right to reach equilibrium. If Q = K, the reaction is at equilibrium. If Q >K, the reaction shifts left.

### Re: Calculating Q

Posted: Thu Jan 24, 2019 2:35 pm
For Q, we can plug in the concentrations of reactants/products at any instant of time. By comparing Q with K, we can predict whether the reaction will move in the forward or reverse direction. If Q< K the reaction will proceed in the forward direction. If Q>K, the reaction will proceed in the reverse direction and if Q=K the reaction is already at equilibrium.

### Re: Calculating Q

Posted: Fri Jan 25, 2019 7:23 pm
The Reaction Quotient (Q) is similar to the Equilibrium Constant (K) in that they are calculated the same way. However, Q only equals K when at equilibrium, it is somewhat like a "temporary" K value. You would need to calculate Q whenever the system is not in equilibrium, or you are unsure whether or not the system is stable.

### Re: Calculating Q

Posted: Fri Jan 25, 2019 8:59 pm
You calculate the reaction quotient (Q) when you are determining which direction the reaction shifts. Q=[Products]/[Reactants] just as K. If Q<K then the reaction shifts right to form towards products and if Q>K then the reaction shifts left to form towards the reactants.

### Re: Calculating Q

Posted: Fri Jan 25, 2019 9:30 pm
You calculate Q when the reaction has been disrupted from equilibrium. Q is similar to K except Q is used to tell which direction the reaction will proceed in order to reach equilibrium.

### Re: Calculating Q

Posted: Sat Jan 26, 2019 8:14 pm
Put simply, Q is calculated when the reaction is not at equilibrium.

### Re: Calculating Q

Posted: Sat Jan 26, 2019 8:54 pm
Q is calculated whenever the equation is not at equilibrium, so if there is a change or anything similar. Also, Q is calculated whenever you are trying to see the result of the reaction (i.e. if the reaction favors the reactants or products).

### Re: Calculating Q

Posted: Sun Jan 27, 2019 3:36 pm
You can calculate Q at any point in the reaction and it will tell you if the reaction is at equilibrium and, if not, which direction the reaction will proceed.