Previously in Chem 104: Kinetics
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Transcript of Previously in Chem 104: Kinetics
Previously in Chem 104:
• Kinetics
TODAY
• A new chapter, a new idea?
A moment of review: Big Ideas in Chemistry
1. Structure determines Behavior
2. Equilibrium and
TODAY
• A new chapter: Equilibrium
• Writing equilibrium expressions
•Disturbing Equilibrium; observing LeChatelier’s Principle
• Calculating equilibrium constants, K
At the end of Kinetics Chapter, this was introduced:
NO + NO N2O2 k1
k-1
Dynamic
applet
At the end of Kinetics Chapter, this was introduced:
NO + NO N2O2 k1
k-1And;
k-1
k1 Keq Backward rate
Forward rateor
What does the value of Keq tell us?
NO + NO N2O2 k1
k-1
If:
10-13 M sec-1
103 M sec-1
Slow backward rate
Fast forward ratelike
Reaction “lies” towards products, Keq is LARGE
What does the value of Keq tell us?
NO + NO N2O2 k1
k-1
If:
10-3 M sec-1
10-13 M sec-1
Fast backward rate
Slow forward ratelike
Reaction “lies” towards reactants, Keq is small:We say reaction doesn’t “go”.
Are rate constants the only way to get Keq?
NO + NO N2O2
For:
Keq [reagents]
[products]
NO !
Keq [NO]2
[N2O2]
More generally Keq is defined as:
aA + bB cC + dD For:
Keq [reagents]
[products]
That’s all you need know in Chapter 16.
Keq [A]a[B]b
[C]c[D]d
What is this Copper experiment about?
Closely followed by
“ a system at equilibrium when disturbed will adjust to remove or minimize the effect of the disturbance”
The series of reactions observed:
3. [Cu(H2O)6]2+ + Cl- [CuCl(H2O)5]2+ + H2O
1. CuCl2(H2O)2(s) + 3H2O [CuCl(H2O)5]+ + Cl-
2. [CuCl(H2O)5]+ + H2O [Cu(H2O)6]2+ + Cl-
What is first equilibrium expression:
[Cu(H2O)6]2+ + Cl-
Keq [reagents]
[products]
Keq [Cu(H2O)62+][Cl]
[CuCl(H2O)5+][H2O]
[CuCl(H2O)5]+ + H2O
Keq [Cu(H2O)62+][Cl]
[CuCl(H2O)5+]
But, pure liquids don’t appear in Keq expression:
The series of reactions observed:
3. [Cu(H2O)6]2+ + Cl- [CuCl(H2O)5]2+ + H2O
Keq [Cu(H2O)62+][Cl]
[CuCl(H2O)52+]
1. CuCl2(H2O)2(s) + 3H2O [CuCl(H2O)5]+ + Cl-
2. [CuCl(H2O)5]+ + H2O [Cu(H2O)6]2+ + Cl-
Keq 0.40M x 7.1 M
0.80 M0.28,
NO UNITS!
Combining reactions equals multiplying K’s
K1eq x K2
eq
(a) CuCl2(H2O)2(s) + 3H2O [CuCl(H2O)5]+ + Cl- K1eq
Net CuCl2(H2O)2(s) + 4H2O [Cu(H2O)6]2+ + 2 Cl- Kneteq
(b) [CuCl(H2O)5]+ + H2O [Cu(H2O)6]2+ + Cl- K2eq
[Cu(H2O)62+][Cl]
[CuCl(H2O)52+
]CuCl2(H2O)2(s)
[CuCl(H2O)52+ [Cl]
[Cu(H2O)62+][Cl]2
CuCl2(H2O)2(s) Kneteq [Cu(H2O)6
2+][Cl]2
Pure solids don’t appear in Keq
What was this Copper experiment about?
Closely followed by
“ a system at equilibrium when disturbed will adjust to remove or minimize the effect of the disturbance”