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Unformatted text preview: 4/9/2009 Free Energy and the Reaction Quotient
G = G(P) – G(R) G(Reactants) G<0 G=0 G>0 G(Products)
©A.Pines,M.Kubinec,UCB ChemQuiz© 30.3 30.3
What are G and K at equilibrium at 25˚C for H2O(l) H2O(g) ? A)
L30-1 Q<K Q=K Q>K GG = = ° + RT lnK = GG° + RT lnQ 0 G<0 K>1 B) G=0 K<1 C) G>0 K<1
L30-2 ©A.Pines,M.Kubinec,UCB ChemQuiz© 30.3 Solution 30.3 ChemQuiz© 30.4
[xi] What are G and K for H2O(l) H2O(g) at 25 ˚C Which is true at t1? A (aq) + 2 B (aq) C (aq)
t1 t A) G<0 K>1 B) G=0 K<1 C) G>0 K<1
L30-3 A) Q > K
©A.Pines,M.Kubinec,UCB B) Q = K C) Q < K
L30-4 ©A.Pines,M.Kubinec,UCB Clarifying Free Energy
• G° G°
– Rxn starts with all reactants and products at 1M or 1atm – Rxn proceeds towards equilibrium Q, K Examples
NaCl (s) Keq ~ 36 Na+ (aq) + Cl- (aq) Na aq) aq) • G
– Starts at whatever conditions specified – Rxn proceeds towards equilibrium
L31-1 • Demo 1: Starting with only products 1M Na+ reacts with 1M Cl- ©Douskey, UCB ©Douskey, UCB L31-2 1 4/9/2009 Chem Quiz 31.1
1M Na+ reacts with 1M ClRight when the solutions are mixed, which is true? A) G<0 Q<K B) G=0 Q=K C) G>0 Q>K
L31-3 Q, K Examples
PbSO4 (s) Pb2+ (aq) + SO42- (aq) Pb aq) aq) -8 (tiny) Keq = 10 (tiny) • Demo 2: Starting with only products 1M Pb2+ reacts with 1M SO42- ©Douskey, UCB ©Douskey, UCB L31-5 H C H H C H H C C H H H Chem Quiz 31.2
Concentration (M) H H C H C H 0.12 1M reacts with 1M Right when the solutions are mixed, which is true? A) G<0 Q<K B) G=0 Q=K C) G>0 Q>K
L31-6 Pb2+ SO42- 0.10 0.08 [cyclopropane] [propene] 0.06 0.04 0.02 0.00 0 5 10 15 20 Time (sec) 25 30 35 40 ©Douskey, UCB ©Douskey, UCB L31-8 Which is true for the reaction at 2 seconds? Q<K Q=K Q>K Which is true for the reaction at 17 seconds? Q<K Q=K Q>K What is the value of the equilibrium constant for the reaction?
©Douskey, UCB L31-9 At 20sec, add propene until concentration is 1M • Immediately after the addition of propene, what is the propene, value of Q? • Which is true immediately after the addition of propene? propene? ∆Grxn < 0 ∆Grxn = 0 ∆Grxn > 0 • What is the direction of change to attain equilibrium? • What are the new concentrations of propene and cyclopropane at equilibrium? * * Note: this is a little more challenging and we’ll get to it soon in class. It’s not on MT3. ©A.Pines,M.Kubinec,UCB L30-15 2 ...
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This note was uploaded on 04/24/2010 for the course CHEM 1A taught by Professor Nitsche during the Spring '08 term at University of California, Berkeley.
- Spring '08