11Announcements - 8/29/02•Thanks for the emails!•Lab reminder-buy lab manual/breakage card soon!-labs start the week of Sept. 9th•Website updates•The first online quiz is available!2Logging on to WebCT¾You will be prompted for a user name and a password•Your user name is your ZOO account name•Your initial passwordis the same as your user name(unless you already have used WebCT)• EXAMPLE: Ima Chemist has a Zoo email address [email protected] Name:ichemistPassword:ichemist(you should change this!)23Combustion4Chemical Change Bonds were broken (H-H and O=O) Bonds were formed (2H-O bonds) The IDENTITIESof the reactant compounds were CHANGED by the processHow does this differ from a purely physical change?35Classifying Matter•Perspectives:Macroscopic Microscopic Particulate•Physical State:Gas Liquid Solid•Pure or Mixture?•Homogeneous or Heterogeneous?6Classification of Matter47Reaction Energetics Energy is consumedto break bonds Energy is releasedwhen making bondsIf Ereleased>Econsumed,HEAT is given off (Thermodynamics!)8Quantifying Chemical Change H2and O2react in a 2:1 ratio to make water-reaction must be balanced(Conservation of Mass)-for a compound, elements always present in definite proportions(Stoichiometry)59Quantifying Chemical Change In our experiment, we had a 1:1 mixture of gases:H2 O2H2 O2BothReact Only ONEReacts(Limiting Reagent) (EXCESS Reagent)10Quantifying Chemical Change Energy release:8.0 x 10-19Joules(for each molecule of O2)In our balloon: 15,000 Joules- about 3.5 KCalories (Kcals)- Calories does not = “Calories”611Gas Properties¾Why did the balloon EXPLODE?-rapidly heated gases-rapid EXPANSIONof gases-explosive shockwave!¾How can we make a biggerexplosion?¾Where did the product (water) go?-2 grams of reactant gases make less than a thimbleful of water-vaporized!12Other Questions: Can the REVERSE reaction occur?2H2O → 2H2+ O2How?713Other Questions: Why doesn’t the H2/O2mixture spontaneouslyexplode (without being ignited)?KINETICS!14Still MoreQuestions! What happened with Balloon III?Two possible reactions:1) 3H2+ N2→ 2NH32) 2H2+ O2→ 2H2O(#1 is too slow; #2 got O2from the air) How do we knowthat atoms and molecules exist?815Some History Democritus-Greek Philosopher (5thCentury B.C.)Asked: “Is there a limit to which something can be divided and yet still remain the same material?”YES!Atomos (“indivisible”)BUT: there was no experimental evidence“Show us!” – Aristotle and Plato16More History Lavoisier-18thCentury Frenchman-Wrote the 1stChemistry text-Considered the “Father of Chemistry”Rigorouslyquantified masses before and after a chemical reaction (in a closed system):Law of Conservation of