Register to reply

What is special about the Avogadro's Constant ?

by Yh Hoo
Tags: avogadro, constant, special
Share this thread:
Yh Hoo
#1
Feb16-12, 07:07 AM
P: 73
6.0221367x10^23 is the avogrado's constant. Does this amount of substances just mean that 6.0221367x10^23 molecules or atoms in gaseous state arrangement will occupy a constant volume provided they are under the same condition(same temperature and pressure) ??
Is it true that the avogadro's constant also imply that with this amount of atoms of same element, they could contribute a mass(g) of exactly a whole number ??
Phys.Org News Partner Chemistry news on Phys.org
Chinese scientists use laser-induced breakdown spectroscopy to identify toxic cooking 'gutter oil'
New insights into 'switchable water' have implications for water purification and desalination
A glucose meter of a different color provides continuous monitoring
Borek
#2
Feb16-12, 08:17 AM
Admin
Borek's Avatar
P: 23,567
Quote Quote by Yh Hoo View Post
Is it true that the avogadro's constant also imply that with this amount of atoms of same element, they could contribute a mass(g) of exactly a whole number ??
No. It will be a mass in g identical to the average atom mass in amu. The latter is a whole number only for a 12C isotope.
Yh Hoo
#3
Feb16-12, 09:08 AM
P: 73
sorry why it will not be a whole number ? wasn't chemist found that 6.02^23 hydrogen atoms will make up 1 g ? so for the atoms of other element which is n times heavier than one-twelfth of the mass of a carbon-12 isotope(or the mass of a hydrogen-1 atom = 1.66 x 10^-27 kg) supposed to have a mass of (n x no. of times heavier than 1/12 of a carbon-12 isotope ) right ? ?

Borek
#4
Feb16-12, 09:20 AM
Admin
Borek's Avatar
P: 23,567
What is special about the Avogadro's Constant ?

Quote Quote by Yh Hoo View Post
sorry why it will not be a whole number ?
Because real elements are mixtures of isotopes, and because of the mass deficit (AKA binding energy) which makes even "perfect" isotopes like 16O to have mass different from exactly 16 amu.
That Neuron
#5
Feb17-12, 09:11 AM
P: 76
The mol is really just a proportionality constant to convert amu to grams.
That Neuron
#6
Feb17-12, 09:12 AM
P: 76
But It looks like Borek already answered that, sorry didn't see your posts, computer page redirected me to advanced reply.
Yh Hoo
#7
Feb18-12, 12:33 AM
P: 73
Quote Quote by Borek View Post
Because real elements are mixtures of isotopes, and because of the mass deficit (AKA binding energy) which makes even "perfect" isotopes like 16O to have mass different from exactly 16 amu.
may i ask what does it means by the mass deficit ? and you mentioned that oxygen-16 isotope has a mass different from exactly 16 a.m.u. but i think oxygen-16 isotope should have a mass of exactly equal to 16.a.m.u. Could you please refer to the attachment i posted and help me to mark my calculation? thanks sir!
Attached Thumbnails
IMG.jpg  
Borek
#8
Feb18-12, 03:20 AM
Admin
Borek's Avatar
P: 23,567
Quote Quote by Yh Hoo View Post
may i ask what does it means by the mass deficit ?
http://lmgtfy.com/?q=mass+deficit
Yh Hoo
#9
Feb19-12, 08:03 AM
P: 73
a new question, is it true that the mass of an atom(atomic mass) is equal to the total mass of of all the protons, neutrons and electrons in that atom ?? and is that the mass of a atom is always constant ??
Borek
#10
Feb19-12, 04:18 PM
Admin
Borek's Avatar
P: 23,567
Quote Quote by Yh Hoo View Post
a new question, is it true that the mass of an atom(atomic mass) is equal to the total mass of of all the protons, neutrons and electrons in that atom ??
No, because of the mass deficit. If you will continue to ignore information you are given nobody will be willing to help you.
Yh Hoo
#11
Mar5-12, 08:49 AM
P: 73
Quote Quote by Borek View Post
No, because of the mass deficit. If you will continue to ignore information you are given nobody will be willing to help you.
im sorry about that because frankly im a A-level student. I have been studying the piece of information that you gave me . Up to this stage i can almost understand the mass defect. But i am still not satisfied with the statement"No other nuclides other than the carbon-12 isotopes have exactly a whole number relative isotopic mass in the scale taking 1/12 of the mass of a carbon-12 isotopes as a standard. ". Because i found that since the relative isotopic mass of nuclides of different isotopes is just a ratio compared to 1u, then there will be other nuclides having a whole number OR non-whole number relative isotopic mass.For example the mass of an oxygen-16 isotope is exactly 16 times greater than 1u. I have showed some evidence by myself. Could you please help me to verify my attachment? Moreover i think that the rest mass of protons,neutron and electron are always constant while static but while moving as in real word the mass decreases. My question is what is the extent the mass will drop to and will it be fluctuating with time ??? i realy need your help
Redbelly98
#12
Mar8-12, 08:35 PM
Mentor
Redbelly98's Avatar
P: 12,069
Quote Quote by Yh Hoo View Post
.For example the mass of an oxygen-16 isotope is exactly 16 times greater than 1u.
According to the links below, the mass of O-16 is 15.9949 u. Close to 16 u, but not exactly.

http://www.wolframalpha.com/entities...n_16/5x/ju/gs/
http://en.wikipedia.org/wiki/Oxygen-16#Table

It is not simply a matter of adding the masses of the protons, neutrons, and electrons. There is an energy change when these particles are combined vs. when they are isolated. The energy change will contribute to the mass of the atom, via the famous relation E=mc2.

If not for this mass-energy equivalence, there would be no energy given off in nuclear reactions.
Yh Hoo
#13
Mar11-12, 11:51 AM
P: 73
Quote Quote by Redbelly98 View Post
According to the links below, the mass of O-16 is 15.9949 u. Close to 16 u, but not exactly.
It is not simply a matter of adding the masses of the protons, neutrons, and electrons. There is an energy change when these particles are combined vs. when they are isolated. The energy change will contribute to the mass of the atom, via the famous relation E=mc2.

If not for this mass-energy equivalence, there would be no energy given off in nuclear reactions.
Thanks so much for your explanation. But could i say that my above attachment is only correct when both the carbon-12 isotope and oxygen-16 isotope are under the same condition, for example both are in isolated form, same temperature and all other possible factors that affects the mass? And one more question, since you said that mass of the atoms are different when in different forms, because of this the unified atomic mass units is apparently a constant but precisely it is a value that keeps on fluctuating at but only at the position of the uncertainties. the same things for the relative isotopic mass of every isotope. They are always fluctuating but only with an extremely minute deficit, is it true??
Yh Hoo
#14
Mar11-12, 01:14 PM
P: 73
Can anyone please show me the working on calculation of relative isotopic mass of any isotope?? thanks a lot!!
Borek
#15
Mar11-12, 01:50 PM
Admin
Borek's Avatar
P: 23,567
Please start a new thread.


Register to reply

Related Discussions
Avogadro constant Chemistry 7
Constant Acceleration: A Special Case Introductory Physics Homework 3
Avogadro's number Classical Physics 2
(special relativity)Trajectory under constant ordinary force Calculus & Beyond Homework 7