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

Calculate ΔHo for the chemical reaction:

  • Thread starter AMan24
  • Start date
  • #1
58
2

Homework Statement


pCfyEeH.png

Homework Equations


5d8vczu.png


The Attempt at a Solution


2(255) - [(1)(159) + (1)(243)]
= +108KJ

The answer key says its b) -108KJ. Am i doing something wrong or is the book wrong?
 
Last edited:

Answers and Replies

  • #2
229
53
When using bond enthalpies, the way you calculate the heat of reaction is
[tex]\Delta H° = \sum \Delta H_{\textrm{Broken}} - \sum \Delta H_{\textrm{Formed}}[/tex]
As in, "the sum of enthalpy changes by broken bonds minus the sum of enthalpy changes by formed bonds." So, the correct answer is -108 kJ.
 
  • Like
Likes AMan24
  • #3
Borek
Mentor
28,441
2,838
ΔH° is not the same thing as a bond enthalpy. Quite the opposite - positive bond enthalpy means negative ΔH° (think why).
 
  • Like
Likes AMan24

Related Threads on Calculate ΔHo for the chemical reaction:

Replies
1
Views
2K
  • Last Post
Replies
3
Views
4K
  • Last Post
Replies
7
Views
4K
  • Last Post
Replies
1
Views
3K
  • Last Post
Replies
2
Views
13K
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
5
Views
2K
  • Last Post
Replies
1
Views
3K
  • Last Post
Replies
3
Views
1K
Replies
1
Views
3K
Top