Initial Concentrations

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Ashley Lopez 3J
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Initial Concentrations

Postby Ashley Lopez 3J » Sun Jan 17, 2021 11:00 pm

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
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Re: Initial Concentrations

Postby Joyce Pang 2H » Sun Jan 17, 2021 11:08 pm

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
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Re: Initial Concentrations

Postby Natalie Do 3F » Sun Jan 17, 2021 11:14 pm

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.

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Re: Initial Concentrations

Postby Simrah_Ahmed1J » Sun Jan 17, 2021 11:14 pm

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
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Re: Initial Concentrations

Postby Carolina Gomez 2G » Sun Jan 17, 2021 11:15 pm

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.

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Re: Initial Concentrations

Postby SophiaJenny3I » Sun Jan 17, 2021 11:16 pm

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.

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Re: Initial Concentrations

Postby Gustavo_Chavez_1K » Sun Jan 17, 2021 11:27 pm

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
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Re: Initial Concentrations

Postby Alejandro Gonzalez 2G » Mon Jan 18, 2021 12:00 am

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

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