## ICE problems

Jasmin Argueta 1K
Posts: 69
Joined: Fri Sep 28, 2018 12:16 am

### ICE problems

In regards to doing ICE problems, I'm a bit confused for the "change" section. I know we are suppose to include coefficients on the x value if there is a molarity given, although how do you know if the x value is positive or negative?

Chem_Mod
Posts: 18400
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 435 times

### Re: ICE problems

If the reaction is going forward, the reactants decrease (negative), and the products increase (positive).

Posts: 62
Joined: Fri Sep 28, 2018 12:23 am

### Re: ICE problems

You are always adding a the change to the concentrations, whether thats positive or negative, it doesn't matter, you will find out after solving. But in terms of weather you are subtracting the x or adding the x, if you are starting with all reactants and no products, you are going to have to subtract from some of the reactants in order to make some products. On the other hand, if you have both an initial concentration of products and reactants, you have find Q and compare it to your K and see which direction the reaction will proceed. That direction will tell you if you subtract a change from your products and add it to reactants and vice versa.

LilyL1C
Posts: 24
Joined: Fri Sep 28, 2018 12:20 am

### Re: ICE problems

It depends on which way the reaction is going.
If it is a forward reaction, then reactants are getting turned into products, so you would subtract the change from the reactants and add the change to the products.
If it a reverse reaction, then the products are getting turned into reactants, so you would subtract the change from the products and add the change to the reactants.

Amar Singh
Posts: 31
Joined: Fri Sep 28, 2018 12:20 am

### Re: ICE problems

Usually you will know in the problem which way the reaction is proceeding. Most of the times it will be the forward reaction that is favored, but occasionally it will be the reverse reaction. Sometimes the concentrations of the products and reactants are given, so you might have to calculate Q and use that to see where the reaction is heading. Once you know that, you can determine which change would be negative and positive. For example, if the forward reaction is favored, then the reactants would be subtracted from (because they are being turned into products), and the products would be added to (because they are being formed).

Emilia z
Posts: 28
Joined: Fri Sep 28, 2018 12:21 am

### Re: ICE problems

The change refers to what change is happening to that species, and we use x because we don’t know the exact amount that changes (either taken away or added/created)