Moles and Chemical Equations

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Brendan Duong 1I
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Moles and Chemical Equations

Postby Brendan Duong 1I » Mon Oct 05, 2020 11:20 am

Are moles equal to stoichiometric coefficients or are they equal to the coefficients times the subscripts?
Given: 2Na+ 2H2O -> 2NaOH +H2
So do we say that there are 2 moles of Hydrogen on the reactant side of the equation, or do we say there are 4
A more in-depth answer than simply 2 or 4 would be appreciated
Edit: Or would it technically be moles of the entire compound, not just the element; so 2moles of h2O?

Mary Gallo 1G
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Re: Moles and Chemical Equations

Postby Mary Gallo 1G » Mon Oct 05, 2020 11:23 am

I believe in this case there are 2 moles of H2O molecules, but there are 4 mol H atoms on the reactant side of the equation. Hope this is helpful!
Last edited by Mary Gallo 1G on Mon Oct 05, 2020 11:25 am, edited 1 time in total.

Ashlen Bullock 1H
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Re: Moles and Chemical Equations

Postby Ashlen Bullock 1H » Mon Oct 05, 2020 11:24 am

From my understanding, they are equal to the moles times the subscripts. So for example, you would say that there are 4 moles of hydrogen on the left and four moles of hydrogen on the right. But I think you only describe it this way if you are explaining conservation of mass.
Last edited by Ashlen Bullock 1H on Mon Oct 05, 2020 11:26 am, edited 1 time in total.

Andrew Wang 1C
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Re: Moles and Chemical Equations

Postby Andrew Wang 1C » Mon Oct 05, 2020 11:24 am

Hi!
The moles of each respective molecule is equal to the stoichiometric coefficient.
The moles of each individual element in a molecule is equal to the stoichiometric coefficient times the subscript.

So for your question, there would be 4 moles of hydrogen atoms, but 2 moles of water molecule.

Hope this helps!

Olivia Yang 3J
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Re: Moles and Chemical Equations

Postby Olivia Yang 3J » Mon Oct 05, 2020 11:31 am

The stoichiometric coefficients for each compound in a balanced chemical equation will be equal to the number of moles of said compound. There are 4 Hydrogen atoms on both the reactant and product side of the equation. In one mole of H2O there will be 2 moles of Hydrogen atoms and 1 mole of oxygen atoms. In this equation there are two moles of H2O on the reactant side and four moles of hydrogen ATOMS on each side.

Cassidy Cheng 1J
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Re: Moles and Chemical Equations

Postby Cassidy Cheng 1J » Mon Oct 05, 2020 11:31 am

Yup, there would be 2 moles of Na, 2 moles of H2O, 2 moles of NaOH, and 1 mole of H2! There would also be 2 moles of H2, 2 moles of O (on the reactants side), and so on.

Kiran Singh 3A
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Re: Moles and Chemical Equations

Postby Kiran Singh 3A » Mon Oct 05, 2020 11:34 am

This can be confusing. You can say 2 moles of H2O on the reactant side, but I think if you wanted to say the quantity of hydrogen you would multiply the 2 moles of H2O by 2 (since the compound contains H2 and not just H) to get 4 moles of hydrogen on the reactant side. Hope that makes sense.

Ashley Ko 3I
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Re: Moles and Chemical Equations

Postby Ashley Ko 3I » Mon Oct 05, 2020 11:37 am

Stoichiometric coefficients can be equated to the number of moles of a reactant and/or product in a chemical equation. For example, the 2 in the chemical equation you gave before the H2O represents two moles of H2O. However, the stoichiometric coefficients can also be used to determine the number of moles of a certain atom or polyatomic ion in a molecule (coefficient times subscript). For instance, if one was trying to find the number of moles of hydrogen in the 2 moles of H2O, then there would be 4 moles of hydrogen (1 mole of H2O has 2 moles of hydrogen; thus, 2 moles of H2O has 4 moles of hydrogen). The main concept is applying molar ratios. Hope this helps answer your question!

Emmeline Phu 1G
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Re: Moles and Chemical Equations

Postby Emmeline Phu 1G » Mon Oct 05, 2020 11:40 am

Hi! In regards to your question, the number of moles is dependent on both the subscript and the stoichiometric coefficients. Both would have to be taken into account when determining the number of moles for an element or compound. There are 4 mol hydrogen on the reactant side because of subscript 2 and the stoichiometric coefficient of 2 (multiplied). So the ratio of hydrogen to H2O would be 4 mol hydrogen to 2 mol H2O. Hope this helps! :)

Sharon Kim 2A
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Re: Moles and Chemical Equations

Postby Sharon Kim 2A » Mon Oct 05, 2020 11:40 am

In some of the more difficult types of problems, would the mass of the products change because some of it will go off as gas?

Steph Du 1H
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Re: Moles and Chemical Equations

Postby Steph Du 1H » Mon Oct 05, 2020 11:44 am

Sharon Kim 1A wrote:In some of the more difficult types of problems, would the mass of the products change because some of it will go off as gas?


Hi. No, due to conservation of mass, the mass of the products do not change. If you were to perform the experiment in a closed beaker where the gas cannot escape the container, then the mass remains the same. If the gas were to escape, then the mass of the products would be less, but that is only because you aren't taking the mass of the gas into account.

aashmi_agrawal_3d
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Re: Moles and Chemical Equations

Postby aashmi_agrawal_3d » Mon Oct 05, 2020 3:43 pm

There are 2 moles of H20 but 4 moles of H.

MMorcus2E
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Re: Moles and Chemical Equations

Postby MMorcus2E » Wed Oct 07, 2020 1:04 pm

Hi!
So the stoichiometric coefficients represent how many of the molecule you are balancing has, like 2 C6H12O6 molecules for example. This changes the number of moles for each individual element. They are very closely related because the stoichiometric coefficients change the number of moles of a given element, but they are not the same.
Hope this helped!


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