ICE box

[605823283]

In the ICE box, how do you know whether to add or subtract x for the change in molar concentration? Is reactants always -x and products are always +x?

[Preston Pham 2H]

No, for me you can determine the change when looking at the initial values they give you. If they give you the initial values of products, then you would put -x for products and plus x for reactants. If they give you the initial values of reactants, then you would put -x for reactants and +x for products.

[Ryan Blaydon 1K]

Yes so what Preston said is correct. The way I look at it is that whatever is being used up is a -X and anything being produced is a +X. Then you just look at the stoichiometric coefficient to determine what number goes in front of the X.

[Gianna Sciole 2F]

it depends on what initial values you are given for what is being used up. the reaction could be going forwards, or it could be a reverse reaction. whatever substance(s) is/are being used up, you will subtract x from, and whatever substance(s) is/are being produced, you will add x to.

[Daljit Takher 1B]

A good example would be the ice box from question 9 in achieve, there you would subtract -2x from the product and add an x to the reactants, since the stoicimentric coefficient is 2 for the product, and in addition more NO is added therefore the reaction is going to result in x being added to N2+O2

[105778693]

You would have to check the values they give in the question itself. If they give product values, the x on the product box in the ICE box would be negative and positive for the reactant boxes. Vice versa for reactant values.

[erud]

It would depend on the initial values from the beginning, favoring either forwards or backwards. Whatever the reactants are are negative x, and products are positive.

[Alice Guey 1B]

So far in our Achieve problems, I have identified two cases when we need to use ICE boxes. In the case that we have initial concentrations of 0 (it can be either on the reactant or product side), we will add +nx to the side with the zero and subtract -nx from the other side. In the case that we are told concentrations are added after equilibrium is already reached, we will subtract -nx from the side where the extra concentrations were added and add +nx to the other side.

[Anubhav_Chandla1G]

In general terms, based on the initial values you are given, if you are given initial values for reactants, then reactants would be negative in the ICE box and products would be positive. On the other hand, if you are given initial values for products, then the reaction would be in reverse, leading to the products being negative and the reactants being positive. Additionally, it can be generalized to say that reactants will usually be negative in the ICE box since they are combining to become products, which generally leads products to be positive since they are being formed in a reaction.

[elletruchan2I]

Usually whether you subtract from reactants or products depends on the context of the problem. Often times it will either tell you, or you have to use Le Chatelier's principle for pressure/volume and changing concentrations.

[Skylar Lo 2C]

It would depend on the molar ratios of the chemical equation.

[205769933]

Hi! It really depends on the Q value, and whether the reactants or products are being used up. If you compare the Q value with K, it should explain which direction the reaction is favoring, and from which side of the reaction to subtract and add to.

[Veronica Larson- 1I]

The -X just represents that some unknown amount is reacting. So, if you start off with a specific amount of reactants (and assuming that the reaction is proceeding in the forward direction), then you would be subtracting X from the reactants.

[Kayla Ziebell 1H]

If something is being used up in the reaction, it is being subtracted out as -x, and if something is being produced in the reaction, it is being added in as +x.

[Emily Nguyen 3L]

No, it doesn't always have to be reactants are -x and products are +x. Whatever you set the reactants to be just has to be the opposite sign as the products, whether it's -x and +x (respectively) or +x and -x.

[Molly Smith 1J]

To figure out whether it is +x or -x, you need to consider what value they gave you for the initial concentration. If they gave you reactant, product would start at zero and would be +x to get the final concentration (if the coefficients are in a 1:1 ratio). If they give you product, then reactant would start at zero and it would be +x for the reactant.

[Nicole Ton 3C]

In the ICE box, you get to define what x is. It isn't always just x; a lot of the time there will be a coefficient in front of the x, which is determined by the molar ratio of the products and reactants in the reaction. Determining which side has -x and which side has +x is based on what you start off with initially. Most times, reactants are -x and products are +x because initially you only have reactants and the concentration of products is 0; so, the change in molar concentration means has to be positive for products because there would be nothing to subtract (concentration can't be a negative number). However, if you are starting with only products and no reactants, then it is possible for products to have -x and reactants to have +x.

[405532435]

For whichever molecule they give uou an initial amount for, you can infer that the other initial amounts are 0. For the one with an inital amount, you can assume you are subtracting x (multiplying whichever coefficient is in front of it). For the other initial amounts that are zero, you are adding x and multiplying it by whichever coefficient is in front of the molecule.
Hope this helps!

[Katryn Heine 3A]

Hi! Normally you subtract x from whatever quantity you're given and you add x to the ones that you're assuming are zero. In a lot of cases, it'll tell you how much of the reactant you have and so that is what you'll subtract x from (and add to the others). Since we're working with equilibrium reactions it can go either way though.

[Polo Morales 3C]

It wouldn't matter too much which one you call -X and which one you call +X, as long as you use them consistently. When you go to solve for X, the +/- sign will be adjusted to show you which concentrations increased and which ones decreased as the reaction advanced. That being said, the math is easier if you make X the change is the concentrations of molecules that are being created, and -x the change in concentration of the molecules that were there initially. Hope this helps!

[Kathleen Wijaya 3L]

You should determine whether the reaction will shift forward to form products (product side will have +x, reactants will have -x) or reverse to form reactants (reactants will have +x, products will have -x)