Chemistry 13Dr. Tom MalloukSection 001 Phone 863-9637MWF 8:00-8:50 am Email: tom@chem.psu.edu

Office hours: M 10-11, T 9-10 (or by appointment) 224 Chemistry

TA: Laurie Heinicke, lah329@psu.edu

TEXTSBrown, LeMay, & Bursten, Chemistry: The Central Science, 9th Ed., 2003 (required)

Supplementary Reading on course website, http://courses.chem.psu.edu/chem13 (required)

Wilson Solutions to Exercises, The Central Science, 9th ed. (recommended)

Chem 12 - Chemical principles• Covered the basics (Ch. 1-4, 10)• Thermochemistry, periodicity, bonding• How structure affects properties and function

Chem 13 - Quantitative understanding of reactions• Will a reaction occur? (thermodynamics)• How fast will it go? (kinetics, nuclear chemistry)• Quantitative equilibria:

Acid-Base, Solubility, Oxidation-Reduction• Inorganic materials, their properties, and applications

“I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind.” - Lord Kelvin, 1883

Lectures in Chem 13

• 3x per week, no recitation• There is no such thing as a stupid question!• In-class problem solving and Friday quizzes• Demonstrations are part of the fun (and also on the

exam!)

Homework

• Is not collected, but is important preparation for on-line quizzes and midterm exams

• Office hours and tutoring sessions are a good time to discuss homework problems

Your grade in Chem 13

• Exams - 70%3 midterms + comprehensive final

• Quizzes - 30%In class and web-based quizzes

Grading scale:A :91, A-:88, B+:85, B:80, B-:77, C+:74, C:65, D:54

See course website for full description: http://courses.chem.psu.edu/chem13

• Interactive Schedule contains links to homework, quizzes, reading, exam locations, lecture notes

• Lecture notes on website - please print and bring to classAlso,• TA contact information• Detailed instructions for on-line quizzes• e-Suggestion box

Four keys to success in Chem 13

• Manage your timeI expect 9-10 hrs per week consistently(lecture, reading, homework, quizzes)

• Come to classSounds obvious (?!)In-class quizzes are part of your grade

• Seek helpDo not wait to get help! If you fall behind in this class, you will be in serious trouble!Get help from me, the TA, and the tutors in the Chemistry Resource Room (211 Whitmore)

• Choose your friends wiselyCooperative study groups - OK to do homework togetherYou must do quizzes on your own.

CHEMICAL KINETICS - Ch. 14

Kinetics is the study of reaction rates.

Thermodynamics tells us if a reaction can occur but not how fast. (More later)

Spontaneous reactions:

H2(g) + 1/2O2(g) H2O(g) (very exothermic, but very slow)

2NO2(g) N2O4(g) (weakly exothermic, but very fast)

Why are reaction rates important?How quickly will food spoil? What can be done to slow or prevent it?

How do life processes (metabolism, respiration, photosynthesis) work? What do enzymes do?

AVERAGE VS. INSTANTANEOUS RATES

Rate: change that occurs in a given interval of time.

Average speed: x / t = rate of travel(change in position over change in time)

rate of school bus = distance traveled = x time t

x = xfinal – xinitial = 4 miles

t = tfinal – tinitial = 2:10 pm - 2:00 pm = 10 min

Speed =

But the instantaneous rate is always changing:0 mph at red light, 60 mpg on highway

instantaneous rate =

dt

dx

t

xt

=

⇒ 0lim

Chemical rate Laws describe instantaneous rates in terms of concentration

time

Sample Question

The slope of the blue line indicated ([X]/t) represents

1. an instantaneous rate

2. an average rate

3. both

4. neither

[ ]t

X

Δ

Δ[X]0

time

t

[X]

[X] Slope of the line is

REACTION RATES

We can express the rate of reaction in terms of:

1. appearance of products2. disappearance of reactants

Stoichiometry of reaction tells us how these are related.

General case:aA + bB cC + dDreactants products

(a, b, c, d are stoichiometric coefficients)

[ ] [ ] [ ] [ ]t

D

dt

C

ct

B

bt

A

arate

Δ

Δ+=

Δ

Δ+=

Δ

Δ−=

Δ

Δ−=

1111

Example2HI(g) H2(g) + I2(g)

6 moles of HI in a 1 L flask are converted to I2 and H2 in 1 min.

What is the rate of disappearance of HI?

What is the rate of appearance of I2? H2?

• Twice the rate of disappearance of HI• 1/2 the rate of disappearance of HI

FACTORS THAT AFFECT THE RATE OF REACTIONS

1. The reactantsChemical identity + physical state(solid, liq, gas, solute, fine particles,…)

2. Concentration of reactantsIncreasing conc. faster rates (usually)

3. TemperatureIncreasing T faster rates (almost always)

4. Presence of a catalyst

Rate Law: relationship between the reaction rate and concentration of the reactants

aA + bB cC + dD reactants products

The rate law is:

rate (= d[A] /dt) = k[A]x[B]y

k is the rate constantindependent of [A] and [B]; varies with T

x and y are exponents ≥ 0, not necessarily integers

EFFECT OF CONCENTRATION

EFFECT OF CONCENTRATIONrate = k[A]x[B]y

Are x, y the same as a, b?Sometimes yes, in general, no (depends on reaction mechanism)

NOTE: dependence of rate on concentration MUST be determined experimentallyIt CANNOT be predicted from overall reaction

experiment rate law mechanism (exponents x, y)

Examples of Rate Laws: Rate = k[A]

= k[B] = k[A]2

= k[A][B]