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”