Chemical Forums

Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: pkeller on October 06, 2009, 10:22:42 AM

Title: Calculating ΔH
Post by: pkeller on October 06, 2009, 10:22:42 AM

Li+Li-(s) → Li(s) + Li(s)

Now consider these reactions and energies:

(i) Li(s) → Li(g), with ΔH = 161 kJ / mol
(ii) Li(g) → Li+(g) + e−, with ΔH = 520.3 kJ / mol
(iii) Li(g) + e− → Li− (g), with ΔH = −56 kJ / mol
(iv) Li+Li− (s) → Li+(g) + Li− (g), with ΔH = 734.7 kJ / mol

Use this information to calculate ΔH for the dilithium destruction reaction below.

Li+Li− (s) Li(s) + Li(s)

 ???

Title: Re: Calculating ΔH
Post by: G O D I V A on October 06, 2009, 10:33:54 AM

I believe that you gotta do hess's law and I get +109.4 kJ/mol?  Is that correct?

Title: Re: Calculating ΔH
Post by: pkeller on October 06, 2009, 10:38:58 AM

Quote from: G O D I V A on October 06, 2009, 10:33:54 AM

I believe that you gotta do hess's law and I get +109.4 kJ/mol?  Is that correct?

yes I think thats the right aswer, could you show how you rearranged the state equations that were given to cancel out. I cant get them to cancel for some reason

Title: Re: Calculating ΔH
Post by: G O D I V A on October 06, 2009, 11:00:24 AM

(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fimg62.imageshack.us%2Fimg62%2F3649%2F42209268.jpg&hash=8fa2bf9ece04902e9fa76353b50eec67f0754c1c)




Red is 520.3
Purple is 734.7
Cyan is -56
Black is 161

Red is wrong way so becomes -520.3
Purple is correct way
cyan is wrong way which becomes 56
Black si wrong way which becomes -161

therefore:

-520.3 + 734.7 + 56 - 161 = +109.4 kJ/mol

Title: Re: Calculating ΔH
Post by: pkeller on October 06, 2009, 11:09:57 AM

Thanks.