Giovanni Anguiano-Gutierrez 3L
Posts: 52
Joined: Thu Jul 25, 2019 12:17 am

For problems using the work function, why do we have to divide by Avogadro's number?

TanveerDhaliwal3G
Posts: 105
Joined: Fri Aug 30, 2019 12:17 am

You usually divide by Avogadro's number when the question gives you the number of molecules and is asking you to find the number of moles of a compound.

Maika Ngoie 1B
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Joined: Fri Aug 02, 2019 12:16 am

TanveerDhaliwal3G wrote:You usually divide by Avogadro's number when the question gives you the number of molecules and is asking you to find the number of moles of a compound.

Remember that avagadro's number (6.626 x 10^23) is the number of molecules or atoms that are in a single mole, so by dividing by this number, you can convert into moles.

Tahlia Mullins
Posts: 105
Joined: Thu Jul 25, 2019 12:15 am

Just a note, Avogadro’s number is actually 6.022*10^23 while planck’s constant is 6.626*10^-34, not to be mixed up! However, these are provided on tests since they are constants.

Sean Sugai 4E
Posts: 56
Joined: Wed Sep 11, 2019 12:17 am

Avogadro's number is used to find the number of objects, molecules, atoms, particles, etc. in one mol of an object. More specifically, there are 6.0221 x 10^23 objects in 1 mole of said objects. Mathematically, Avogadro's number is used in a ratio to convert the number of moles to the number of objects or from the number of objects to the number of moles. The equation in the textbook is N=nNa, where N is the number of objects, n is the number of moles, and Na is Avogadro's number.

When it comes to problems regarding work function, however, you would use Planck's constant, h, which is 6.626 x 10^-34 (J)(s).

Also, consider the units. While Avogadro's number has units such as molecules, objects, atoms, particles, etc., Planck's constant is joules times seconds, which makes sense given the equation: E=hv, where h is Planck's constant and v is the frequency. If E is measured in joules and v is measured in hertz (1/s), then Planck's constant has to be (Joules)(seconds). It's always a good idea to check units to make sure the math is correct.

There are instances in which the question asks for the energy per mole of photons. This means that you have to multiply Avogadro's number by the energy of the photon, so E(per mole of photons)=NaE(1 photon). . However, this would potentially require you to find the energy of the photon, which can be found using E=hv, where h is Planck's constant and v is the frequency. Thus, in some cases, you will have to use both Planck's constant and Avogadro's number. It just depends on the question being asked, so read carefully!
Last edited by Sean Sugai 4E on Sun Oct 13, 2019 8:30 pm, edited 1 time in total.

Omar Selim 1D
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Joined: Sat Jul 20, 2019 12:16 am

Avogadro's number = 6.022 * 10^23 is the number of atoms in a mole. This is used to determine moles of a substance when given the amount of molecules.

JasonKwon_3k
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Joined: Thu Jul 11, 2019 12:16 am

You divide by Avagadro's number to find the answer in relation to one atom/photon, which is usually how the questions will be phrased.

Darren Nguyen 1F
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