Chemistry 13 Dr. Tom Mallouk Section 001Phone MWF 8:00-8:50 am Office hours: M 10-11, T 9-10 (or by appointment) 224 Chemistry TA: Laurie Heinicke, TEXTS Brown, LeMay, & Bursten, Chemistry: The Central Science, 9th Ed., 2003 (required) Supplementary Reading on course website, (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: Interactive Schedule contains links to homework, quizzes, reading, exam locations, lecture notes Lecture notes on website - please print and bring to class Also, TA contact information Detailed instructions for on-line quizzes e-Suggestion box
Four keys to success in Chem 13 Manage your time I expect 9-10 hrs per week consistently (lecture, reading, homework, quizzes) Come to class Sounds obvious (?!) In-class quizzes are part of your grade Seek help Do 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 wisely Cooperative study groups - OK to do homework together You 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: H 2 (g) + 1/2O 2 (g) H 2 O(g) (very exothermic, but very slow) 2NO 2 (g) N 2 O 4 (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 = x final – x initial = 4 miles t = t final – t initial = 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 =
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 [X] 0 time tt [X][X] [X] Slope of the line is
REACTION RATES We can express the rate of reaction in terms of: 1.appearance of products 2.disappearance of reactants Stoichiometry of reaction tells us how these are related. General case: aA + bB cC + dD reactants products (a, b, c, d are stoichiometric coefficients)
Example 2HI(g) H 2 (g) + I 2 (g) 6 moles of HI in a 1 L flask are converted to I 2 and H 2 in 1 min. What is the rate of disappearance of HI? What is the rate of appearance of I 2 ? H 2 ? 1.Twice the rate of disappearance of HI 2.1/2 the rate of disappearance of HI
FACTORS THAT AFFECT THE RATE OF REACTIONS 1.The reactants Chemical identity + physical state (solid, liq, gas, solute, fine particles,…) 2. Concentration of reactants Increasing conc. faster rates (usually) 3. Temperature Increasing 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 constant independent of [A] and [B]; varies with T x and y are exponents ≥ 0, not necessarily integers EFFECT OF CONCENTRATION
rate = 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 experimentally It 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]