March 28, 2024, 08:58:25 AM
Forum Rules: Read This Before Posting


Topic: Semiempirical Mass Equation homework problem  (Read 7414 times)

0 Members and 1 Guest are viewing this topic.

mjfranklin

  • Guest
Semiempirical Mass Equation homework problem
« on: September 23, 2006, 08:15:46 PM »
The homework question reads:

"Use the semiempirical mass equation to compute, for given A, the relation between Z and N for a nucleus that has Sn=0 (the neutron "drip line").  Compute N/Z for A=100."

Using Sn=Btot(A,Z) - Btot(A-1,Z), I have been trying to manipulate the equation so that I can plug in A=N+Z for one of the A values to get N/Z=some A dependent expression.  I and several other students have spent hours manipulating the equation every way we can think of, and nothing looks even close to useful for getting an N/Z relationship. 

Are we missing something?

Any suggestions would be really appreciated.


Offline Mitch

  • General Chemist
  • Administrator
  • Sr. Member
  • *
  • Posts: 5298
  • Mole Snacks: +376/-3
  • Gender: Male
  • "I bring you peace." -Mr. Burns
    • Chemistry Blog
Re: Semiempirical Mass Equation homework problem
« Reply #1 on: September 23, 2006, 11:03:22 PM »
You just need an equation in terms of N's and Z's only. You do not need to manipulate the equation into something that looks like N/Z = blah...blah...
« Last Edit: September 24, 2006, 12:18:51 PM by Mitch »
Most Common Suggestions I Make on the Forums.
1. Start by writing a balanced chemical equation.
2. Don't confuse thermodynamic stability with chemical reactivity.
3. Forum Supports LaTex

Offline Mitch

  • General Chemist
  • Administrator
  • Sr. Member
  • *
  • Posts: 5298
  • Mole Snacks: +376/-3
  • Gender: Male
  • "I bring you peace." -Mr. Burns
    • Chemistry Blog
Re: Semiempirical Mass Equation homework problem
« Reply #2 on: September 23, 2006, 11:07:21 PM »
The N/Z is brought up since we know stable nuclei at around A=100 typically have an N/Z ratio of ~1.3. But, at the neutron drip line the ratio becomes roughly ~1.7. This is the point the problem is subtly trying to make you discover from first princibles.
Most Common Suggestions I Make on the Forums.
1. Start by writing a balanced chemical equation.
2. Don't confuse thermodynamic stability with chemical reactivity.
3. Forum Supports LaTex

Offline timmy04jc

  • Very New Member
  • *
  • Posts: 2
  • Mole Snacks: +0/-0
Re: Semiempirical Mass Equation homework problem
« Reply #3 on: September 24, 2006, 01:43:18 AM »
  Hey, Mitch. I'm also having much trouble with #7 of problem set #3. It gets much messier and longer than I thought. You've worked it out already, right? Could you give us any suggestions for making the math shorter/cleaner? Thanks.

Offline Mitch

  • General Chemist
  • Administrator
  • Sr. Member
  • *
  • Posts: 5298
  • Mole Snacks: +376/-3
  • Gender: Male
  • "I bring you peace." -Mr. Burns
    • Chemistry Blog
Re: Semiempirical Mass Equation homework problem
« Reply #4 on: September 24, 2006, 01:51:25 AM »
Quote
You just need an equation in terms of N's and Z's only.

Quote
You do not need to manipulate the equation into something that looks like N/Z = blah...blah...
« Last Edit: September 24, 2006, 12:18:36 PM by Mitch »
Most Common Suggestions I Make on the Forums.
1. Start by writing a balanced chemical equation.
2. Don't confuse thermodynamic stability with chemical reactivity.
3. Forum Supports LaTex

Sponsored Links