announcements reminder- exam #3 is one week from today (april 23 rd ) review session: wednesday,...

ANNOUNCEMENTSANNOUNCEMENTS•Reminder- Exam #3 is one week from today (April 23rd)

Review session: Wednesday, April 21st @ 5:00pm

When is the next exam?When is the next exam?

1 2 3 4

78%

16%

3%3%

1. One week from today

2. Two weeks from today

3. Next Wednesday

4. May 14th

The rate law for an elementary The rate law for an elementary step is given by the equation for step is given by the equation for that stepthat step

Elementary Step Molecularity Rate Equation

A → product Unimolecular Rate= k[A]

A + B → product Biomolecular Rate= k[A][B]

A + A → product Bimolecular Rate= k[A]2

2A + B → product Termolecular Rate= k[A]2[B]

Example: Ozone depletion by CFC’sExample: Ozone depletion by CFC’s

Cl + O3 → ClO + O2

ClO + O → Cl + O2

Overall reaction:Intermediate?Catalyst?

How to determine if a proposed reaction How to determine if a proposed reaction mechanism is “reasonable”mechanism is “reasonable” HH22 + 2ICl + 2ICl → → 2HCl + I2HCl + I22

Proposed mechanism 1:

Step 1:

H2 + ICl → HI + HCl (slow)

Step 2:

ICl + HCl → HI + Cl2

Sum

Rate

Step 1

Step 2

Overall

Proposed mechanism 2:

Step 1:

H2 + ICl → HCl + HI (slow)

Step 2:

HI+ ICl → HCl + I2

Sum

Rate

Step 1

Step 2

Overall

Two mechanisms for determining Two mechanisms for determining mechanismsmechanisms

1. Determine and interpret rate law

2. Isotopic Labeling

CHAPTER 15CHAPTER 15

EQUILIBRIA

Alcohols can be made from alkenes Alcohols can be made from alkenes and alkenes can be made from and alkenes can be made from alcoholsalcoholsAlkene→ Alcohol

Alcohol→ Alkene

Mechanism:

The principle of microscopic The principle of microscopic reversibilityreversibility

What is the equilibrium expression What is the equilibrium expression forfor Fe Fe22SS33(s) 2 Fe(s) 2 Fe3+3+(aq) + 3 (aq) + 3 SS2-2-(aq)(aq)

1 2 3 4

25% 25%25%25%1. 1:

2. 2:

3. 3:

4. 4:

][

]][[

32

23

SFe

SFeK

][

][][

32

3223

SFe

SFeK

]][[ 23 SFeK

3223 ][][ SFeK

Manipulating Equilibrium Expressions:

N2(g) + 3 H2(g) 2 NH3(g) K = =5.5 x 105

Reversing Reactions

Multiplying by a Factor

322

23

]][HN[

]NH[

Manipulating Equilibrium Expressions:

Adding Reactions

Cu(OH)2(s) Cu2+(aq) + 2 OH-(aq) K1 = 1.6x 10-19

Cu2+(aq) + 4 NH3(aq) Cu(NH3)42+(aq) K2 = 1.2 x 1012

Cu(OH)2(s) + 4 NH3(aq) Cu(NH3)42+(aq) + 2 OH-(aq) K = ?

Cu(NHCu(NH33))442+2+(aq) (aq) Cu Cu2+2+(aq) + 4 NH(aq) + 4 NH33(aq) K (aq) K

= 8.5 x 10 = 8.5 x 10-13-13

If [CuIf [Cu2+2+] = 1.0 x 10] = 1.0 x 10-6-6 , [NH , [NH33] = 1.0 x 10] = 1.0 x 10-3-3, , [Cu(NH[Cu(NH33))44

2+2+], then …], then …

1 2 3

33% 33%33%1. It is at equilibrium

2. Reaction goes forwards

3. Reaction goes backwards

Equilibrium Calculations: Your Pathway to Equilibrium Calculations: Your Pathway to HappinessHappiness

1. Write the equilibrium expression2. Determine Q

1. if Q = K, it’s at equilibrium2. if Q < K, reactants go to form products3. if Q > K, products go to form reactants

3. Call the amount reacting “x”4. Solve for x in the equilibrium expression5. Use x to determine equilibrium concentrations

Given these initial concentrations, what will the final concentrations be when equilibrium is reached?

K in terms of pressure: Kp vs. Kc

Kp = Kc(RT)n

n = change in numbers of moles of gas

2 NH3(g) N2(g) + 3 H2(g) Kc = 5.8 x 105

Kp =

LeChatelier’s Principle: Doing the math

1-Liter flask contains 0.50 mol butane and 1.25 mol isobutane (at equilibrium).

0.50 mol butane are added. What happens, and what is the result?