|Aug16-05, 10:52 AM||#1|
this is homework problem i'm having some trouble with... i haven't had chemistry yet so i'm not sure how i could convert atoms into kg, and the textbook i have doesn't do any examples of problems like this one... i don't even know where to begin.
Deuterium (A=2, Z=1) is an attractive fuel for fusion reactions because it is abundant in the waters of the oceans. In the oceans, about 0.015% of the hydrogen atoms in the water (H2O) are deuterium atoms.
(a) How many deuterium atoms are there in 4 kilogram of water?
(b) If each deuterium nucleus produces about 7.4 MeV in a fusion reaction, how many kilograms of ocean water would be needed to supply the energy needs of the United States for one year, estimated to be 9.3 1019 J? (answer should be in kg)
|Aug16-05, 11:19 AM||#2|
|Aug16-05, 11:51 AM||#3|
i tried the first part but i'm not sure if this is what you meant...
molecular weight of water = 18 g/mol = .018 kg/mol
2(.018kg/mol) = .036 hydrogen atoms in 1 kg of water
4kg(.036) = .144 hydrogen atoms in 4 kg of water
.00015(.144) = 2.16e-15 number of deutrerium atoms in 4kg of water
don't i need to use the avagadros number someplace?
|Aug16-05, 12:04 PM||#4|
Yes, one needs to use Avogadro's number.
1 gram-mole = 6.022E23 atoms or molecules.
1 kg-mole = 6.022E26 atoms or molecules.
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