Initial Concentrations

[Ashley Lopez 3J]

How do we know when we are suppose to put the actual values of initial concentrations and not as 0 as seen in Sapling hw #10? I was confused as to why we put the initial values for both reactant and product.

[Joyce Pang 2H]

You place values in the ICE table as they are given. If a question gives an initial value for concentration and asks for the final concentration, you'd use the initial value of concentration for whichever reactant it is, and use 0 for your products because no products have been formed yet. Putting all the values just makes it easier to visualize and comprehend what the change is and where it's occurring.

[Natalie Do 3F]

Putting concentrations like that, like what Joyce said, is mostly about being able to visualize the direction of the reaction. In #10 there is only one reactant and one product so it is easy to calculate.

[Simrah_Ahmed1J]

Im assuming you're talking about week one sapling problem 10, but basically for this problem you obviously have calculate the k value from the given equilibrium concentrations, then it asks you to calculate the equilibrium concentrations of the two when 1 mol of NO₂ is added after the system is already at that equilibrium concentrations they were at.
So those given concentrations were 0.477 mol/L N₂O₄ and 2.31 mol/L NO₂, so you just add 1 mol of NO₂, and start off your ICE box with 0.477 mol/L N₂O₄ and 3.31 mol/L NO₂. Which is contrary to what you're often used to starting with 0 concentration of the products.

[Carolina Gomez 2G]

The initial value will be 0 if that is what is being formed. For example, if you place a certain amount of moles of reactants in an empty container, they will form products. The initial concentration for the reactants would be the molarity (moles/volume) of the moles given in the question and the products will be zero because initially no products have formed.

[SophiaJenny3I]

Hi! You just have to look at what's given to you. Since in #10 you are given both initial concentration, plug those into the ICE table and work from there. I've found that these problems make a lot more sense when you write out everything you know, and then begin to fill in the blanks to figure out what you need to calculate. Often times, if a product concentration is not given, it is 0, before equilibrium, as product has not formed at the start of the reaction. However, if the problem specifies otherwise, go with that.

[Gustavo_Chavez_1K]

We are usually given the initial concentrations of the reactants and so we put those in the ICE table. For the most part the reactants will be 0 if we are not given them since it is basically saying that they have not been formed yet.

[Alejandro Gonzalez 2G]

We are usually given some of the initial molar concentrations, as they usually indicate the reactants that form the product.