Chemical Forums

Please login or register.

Login with username, password and session length

Sponsored links

Pages: [1]   Go Down

Author Topic: When are delta E & delta H equal?  (Read 37232 times)

0 Members and 1 Guest are viewing this topic.


  • Regular Member
  • ***
  • Mole Snacks: +1/-1
  • Offline Offline
  • Posts: 25
When are delta E & delta H equal?
« on: November 23, 2007, 04:34:38 PM »

The question is "Under what circumstances are delta E & delta H essentially equal.  Using the equation delta H = delta E + PV.  Delta E & H will essentially be equal when there is no change in volume.  This part I understand, but the solutions manual adds

"Delta H & delta E are nearly equal when there are no gases in a chemical reaction..."  Why is it only with gases?  In a reaction, solids and liquids also change forms (like ice to water) & have a change in volume.  So am I just getting confused with concepts, or is the book trying to point out something I'm not seeing?


  • Retired Staff
  • Sr. Member
  • *
  • Mole Snacks: +481/-21
  • Offline Offline
  • Gender: Male
  • Posts: 3196
  • Physical Biochemist
Re: When are delta E & delta H equal?
« Reply #1 on: November 23, 2007, 06:20:17 PM »

The change in volume between solids and liquids is negligible.  For example, when 1 mol of liquid water becomes 1 mol of ice at 1 atm pressure, pΔV is about 0.15J/mol, whereas most ΔH and ΔE values are in the hundreds of kJ/mol.

Pages: [1]   Go Up

Mitch Andre Garcia's Chemical Forums 2003-Present.

Page created in 0.068 seconds with 23 queries.