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### AuthorTopic: Clausius-Clapeyron: Ea or dH?  (Read 1965 times) !function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="https://platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); (function() {var po = document.createElement("script"); po.type = "text/javascript"; po.async = true;po.src = "https://apis.google.com/js/plusone.js";var s = document.getElementsByTagName("script")[0]; s.parentNode.insertBefore(po, s);})();

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#### Diamonds

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##### 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?
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#### formaldehyde23

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##### 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.
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#### Diamonds

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##### 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?
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#### formaldehyde23

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##### Re: Clausius-Clapeyron: Ea or dH?
« Reply #3 on: February 20, 2013, 06:34:44 PM »

Yes, exactly.
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#### Sophia7X

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##### 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.
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