+870 Uranium 234 has a half-life of 245 500 years;
We'll imagine we've got a chunk of uranium that contains 3 moles of 234U; we'll assume that it's ONLY 234U, and we won't care about the electrons, we're only gonna concentrate on the nuclei.
N.B.: If you find such a chunk of uranium, please don't touch it, it's radioactive; so don't be stupid and if you find uranium, RUN AWAY.
We wanna know how many uranium nuclei we've got left after :
N.B.: It's just some "brain food", I already have the answer
OK, EinsteinJr. Will take a kick at it!.
Since 1 mole of any element has=6.0221415e+23 atoms, then 3 moles will contain:
6.0221415e+23 x 3 =1.80664245e+24 atoms
1) After one half-life, it should have left=[1.80664245e+24] / 2 =9.03321225e+23 atoms.
2) After 2 half-lives, it should have left =[1.80664245e+24] x 2^-2=4.516606125e+23 atoms.
3)After 3.5 half-lives,,,,,,,,,,,,,,,,,,,,,,,,,,,,,=[1.80664245e+24] x 2^-3.5=1.596861e+23 atoms.
4) After 1 billion years,,,,,,,,,,,,,,,,,,,,,,,,,,=[1.80664245e+24] x 2^-4,073.32=0 atoms.
5) After 2.45 x 10^8 years,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,=0 atoms.
P.S. With the number of atoms that we start with(1.81 x 10^24) and a half-life of only 245,500 years, then it takes less than 80 half-lives or just under 20 million years for the complete decay of the element.
+870 That's right, your answers are exact!
Here's a brownie for getting all questions all right:
