• Support PF! Buy your school textbooks, materials and every day products Here!

Chemistry- boiling point

  • Thread starter Dell
  • Start date
  • #1
590
0
find the boiling point of HF according to the following reaction

HF(L) --> HF(G)
ΔH=7.53 [KJ/mol]
ΔSsys=0.0257[KJ/(mol*K)]

i used the equation

ΔH=-ΔS*T
>>T=-ΔH/ΔS
>>T=-0.0257/7.53

T=-292.996°K

surely this is meant to be positive ???
have i used the wrong equation?? which other equation should i have used?
 

Answers and Replies

  • #2
Mapes
Science Advisor
Homework Helper
Gold Member
2,593
17
Where does ΔH=-ΔS*T come from? Surely ΔG=0 at a phase equilibrium at constant temperature and pressure.
 
  • #3
590
0
i dont know, i have it written in my workbook, could it be a mistake??

if ΔG=0
ΔG=H-ΔS*T
H=ΔS*T

and then it all works fine,,, but how do i know that ΔG=0,?

is there no equation that ΔH=-ΔS*T?/
 
  • #4
Mapes
Science Advisor
Homework Helper
Gold Member
2,593
17
how do i know that ΔG=0,?
This is a condition that applies to any two systems at equilibrium at constant pressure and temperature. It's derived in intermediate thermodynamics as a consequence of the first and second laws.

is there no equation that ΔH=-ΔS*T?/
There could be, but I haven't seen it, and it doesn't apply here.
 

Related Threads for: Chemistry- boiling point

  • Last Post
Replies
9
Views
767
  • Last Post
Replies
3
Views
9K
  • Last Post
Replies
1
Views
1K
  • Last Post
Replies
1
Views
9K
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
3
Views
702
  • Last Post
Replies
1
Views
3K
  • Last Post
Replies
5
Views
4K
Top