Class Notes (836,580)
Canada (509,856)
Chemistry (1,145)
CHEM 204 (19)

34- Gibbs Energy and Equilibrium.docx

3 Pages
Unlock Document

CHEM 204
Christopher Barrett

CHEM 204 04/05/2013 Lecture 34 Martin M. PHGY Tutor Gibbs Energy and Equilibrium How are Δ R and Δ G°Rrelated? We have to use the reaction quotients Q and K. Where Q = [C][D]/[A][B] = P P / C PD A B (for gasses using partial pressures). This gives us the result thatRΔ G = ΔRG° + RT lnQ. At equilibrium this Q becomes the equilibrium constant, K. At equilibrium R G° = – RT ln K. This simple equation can be used to predict the equilibrium of anything with a Gibbs energy. Practical example: What is the vapour pressure of water at 25°C? the ΔVAPG° of water is ΔG°(g) – ΔG° (l) = 8.5 kJ/mol ( )( ) This is the vapour pressure at 25°C, 0.032 bar or 3.2% humidity. Everything in the weather is relative to this 3.2% humidity. So when you say 100% humidity, you really mean 3.2% absolute. This formulae predicts that everything, liquid or solid, evaporates! And this is completely true. If -58 we take gold, which has a ΔG°(sublime) = +326kJ/mol and find K, we find that K = 4.7 10 . This number is so small that it is irrelevant. We can apply this formula better by finding the 3 vapour pressures of different substances. Let's assume we have a room of 100m , meaning 4000 moles of an ideal gas. Substance K Amount in air Water 0.032 2.3 kg Benzene 0.13 41.3 kg Hg 0.0000022 1.8 g The equilibrium constant, K = e –ΔG°/R, will always be reached no matter what side we approach from. If we add more A to the mixture, we get driven to B and vice versa. The number of molecules is not fixed, but the ratio is. We can add or subtract molecules from a reaction and the system will re-establish the equilibrium with Le Chatelier's principle. Let's take an example: A (liq)  B (liq) 100 mol of pure A is placed in a container at 310K, and the reaction is allowed to proceed to equilibrium. The ΔG° = –2830 J/mol. Solving for lnK, Or ln(B/A), we get 3.0. This means there is always 3 times as much B as A in equilibrium. CHEM 204 04/05/2013 Lecture 34 Martin M. PHGY Tutor The fraction and ratio of A will always be the same! Moles added Ratio? Moles of B Moles of A 100 3.0 75 25 +20 (120) 3.0 90 30 -40 (80) 3.0 60 20 Adding some reactant
More Less

Related notes for CHEM 204

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.