Chemical Forums

Please login or register.

Login with username, password and session length

Sponsored links

Pages: [1]   Go Down

Author Topic: Clausius-Clapeyron: Ea or dH?  (Read 531 times)

0 Members and 1 Guest are viewing this topic.

Diamonds

  • Regular Member
  • ***
  • Mole Snacks: +1/-3
  • Offline Offline
  • Posts: 23
Clausius-Clapeyron: Ea or dH?
« on: February 20, 2013, 03:42:04 PM »

Hi guys,

I have seen the Clausius-Clapeyron equation expressed as:

ln(P1/P2) = ΔH / R  (1/T2 - 1/T1)
ln(K1/K2) = ΔH / R  (1/T2 - 1/T1)
ln(K1/K2) = Ea /  R  (1/T2 - 1/T1)

which is right? If they are all right (because all have worked in different cases), doesn't that mean that ΔH = Ea?
Logged

formaldehyde23

  • Regular Member
  • ***
  • Mole Snacks: +1/-7
  • Offline Offline
  • Posts: 23
Re: Clausius-Clapeyron: Ea or dH?
« Reply #1 on: February 20, 2013, 05:56:58 PM »

The only one of the three equations that is the Clausius-Clapeyron equation is the first one, which relates pressure and temperature.
I do not think the second equation exists.
The third equation is the Van't hoff's equation, which relates the rate constant and temperature.
But, no dH is definitely not equal to Ea. Think about a simple reaction. dH is the change in enthalpy of the products and reactants. However, Ea is the minimum amount of energy needed to convert a reactant into a product.
Logged

Diamonds

  • Regular Member
  • ***
  • Mole Snacks: +1/-3
  • Offline Offline
  • Posts: 23
Re: Clausius-Clapeyron: Ea or dH?
« Reply #2 on: February 20, 2013, 06:03:47 PM »

So if a question involves pressures, I use the Clausius-Clapeyron equation to find out ΔHvap, and if it asks about activation energy, I use the Van't Hoff equation to find out the Ea?
Logged

formaldehyde23

  • Regular Member
  • ***
  • Mole Snacks: +1/-7
  • Offline Offline
  • Posts: 23
Re: Clausius-Clapeyron: Ea or dH?
« Reply #3 on: February 20, 2013, 06:34:44 PM »

Yes, exactly.
Logged

Sophia7X

  • Full Member
  • ****
  • Mole Snacks: +32/-4
  • Offline Offline
  • Gender: Female
  • Posts: 249
  • I, a universe of atoms, an atom in the universe.
Re: Clausius-Clapeyron: Ea or dH?
« Reply #4 on: February 20, 2013, 11:39:02 PM »

No, the second equation definitely does exist and that is the Van't Hoff equation.

The third equation is the Arrhenius equation which does not involve K but k, the rate constant.
Logged
Entropy happens.
Pages: [1]   Go Up
 

Mitch Andre Garcia's Chemical Forums 2003-Present.

Page created in 0.055 seconds with 23 queries.