How much energy in MeV is released to form one atom of 87Rb from protons, electrons, and neutrons if the nucleus has a mass of 86.909187 amu? The masses of the proton, electron and neutron are 1.00728 amu, 0.000549 amu and 1.00867 amu, respectively. 1.602x10-13 J = 1 MeV; 1 amu = 1.66054x10-27 kg
I know how to do half of this but I'm having trouble with the other half. I know that I have to find the number of protons, neutrons, and electrons of the element given, then multiply by the corresponding mass. then find change in amu. from there to convert to kg I divide by a thousand. All these calculations bring me to .01229, I'm not sure what's next.
I can't follow what you've done.
I have mass p + mass N + mass e = 87.723173 and that - 86.909187 = 0.813986 amu and that converted to kg = 1.3516563E-27 kg.
Let me know if we are on the same page to this point and please show your work for as far as you are and we can finish.
No it seems we aren't.
So this is what I did to find the P E N of Rb
#protons=#electrions=37 (from the periodic table)
Neurtrons= 87-37=50
with that I multiplied by their masses. Added them together to get 74.6176.
Then I did 86.909187-74.6176 = .01229
or no it equals to 12.29. Then i divided it by 1000 because I thought that's how I would get kg
87 is right. 37 and 50 are right
Check your numbers for PEN. You can't possibly get 74 something. 50 x 1+ is about 50. 37 x 1+ = about 37 and add in a pinch for electron mass and you have AT LEAST 50+37+pinch = 87. And it can't be less than 86.909187 because it LOSES mass when PEN are combined. Get back to me when you check those values and add them. You can check if we agree because I gave you the total mass I calculated in the first response. I also gave you the difference in amu and the number when converted to kg. Then you go from kg to E = mc^2 to get joules; finally, convert J to MEV.
By the way, it's past my bed time but I'll be around tomorrow.
Oh ok, I see what I did wrong, I switched the masses for Electron and Neutron. Ok now we're on the same page. So then to get kg you multiplied 0.813986 amu by 1.66054x10-27 kg = 1.3516563E-27 kg.
Then, plug it into the equation E=mc^2
I got 1.216E-10 .
Then divide that by 1.602x10-13 J to get 759.35 MeV
You have it. Good.
For E I have 1.2148E-10. Probably we used different value for c. I used 2.99792458E8 m/s for a final answer of 758.3 MeV.