Avogadro's Theory

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Homework Statement


This question might sound confusing, because my teacher said it only once, and I don't think I have it down right. So if the question is confusing but you know what I'am trying to get at, please say so. The question is: According to Avogadro's Theory, how are the number of molecules and atoms related in a chemical equation?


Homework Equations


I don't think equations are necessary.


The Attempt at a Solution


I think that the number of molecules would be the same as the number of atoms in a chemical equation, but I'am not sure.
 

Answers and Replies

  • #2
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I think I understand your question

Avogadro's number = 6.022 x 10^23 "things" = 1 mole

1.the "things" may be ATOMS if the substance is an ELEMENT

so 6.022 x 10^23 "ATOMS" = 1 mole of an ELEMENT

2. the "things" may be MOLECULES if the substance is a COMPOUND (molecular to be precise)

so 6.022 x 10^23 "MOLECULES" = 1 mole of an COMPOUND

For the equation:

Si + O2 ---> SiO2

1 mol Si + 1 mol O2 ---> 1 mol SiO2

6.022 x 10^23 "ATOMS" Si + 6.022 x 10^23 "MOLECULES" O2 ---> 6.022 x 10^23 "MOLECULES" SiO2

If this is not what you mean, then pls ask again, it may be related to the other aspect of Avogadro's principle of gases and equal volumes of gases = equal volumes of moles


(my example is just to illustrate the point, even though also SiO2 really exists as a network solid so its stretching it a bit to think of it as a single molecule)
 
  • #3
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Thanks for the explanation. You cleared up a lot of the confusion I had. Can you also explain the other aspect of Avogadro's principle of gases and equal volumes of gases = equal volumes of moles that you mentioned please?
 
  • #4
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glad you got the first part


Avogadro's principle (this he really did - Avogadro's number he never calculated - they just honored him with it since the Principle led others to the huge number)

Comparing gases AT THE SAME TEMP AND PRESSURE (same conditions - not necessarily at STP) in a reaction mixture...

- the volume of Gas A will have the same number of molecules (or can say moles) of Gas B if Gas B has the with the same volume as Gas A

Classic example:

H2 + Cl2 ---> 2HCl

coefficients 1 1 2
volumes (eg. in L) 1L 1L 2L
molecules/mole 1 1 2



or N2 + 3H2 ---> 2NH3

coefficients 1 3 2
volumes (eg. in L) 1L 3L 2L
molecules/mole 1 3 2


so we can predict the volumes of gases using stoichiometry

just remember this works ONLY if the gases are under the same conditions
 

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