* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Survey

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts

Electrolysis of water wikipedia, lookup

Chemical bond wikipedia, lookup

Hypervalent molecule wikipedia, lookup

Rutherford backscattering spectrometry wikipedia, lookup

Thermodynamics wikipedia, lookup

Determination of equilibrium constants wikipedia, lookup

Biochemistry wikipedia, lookup

Computational chemistry wikipedia, lookup

Multi-state modeling of biomolecules wikipedia, lookup

IUPAC nomenclature of inorganic chemistry 2005 wikipedia, lookup

History of chemistry wikipedia, lookup

Photosynthetic reaction centre wikipedia, lookup

Marcus theory wikipedia, lookup

Hydrogen-bond catalysis wikipedia, lookup

Lewis acid catalysis wikipedia, lookup

Rate equation wikipedia, lookup

Process chemistry wikipedia, lookup

Click chemistry wikipedia, lookup

Isotopic labeling wikipedia, lookup

Chemical reaction wikipedia, lookup

Molecular dynamics wikipedia, lookup

Bioorthogonal chemistry wikipedia, lookup

Chemical thermodynamics wikipedia, lookup

Physical organic chemistry wikipedia, lookup

Chemical equilibrium wikipedia, lookup

Stoichiometry wikipedia, lookup

Transition state theory wikipedia, lookup

Transcript

Announcements…Monday April 15 We are now in Chapters 8-9 all sort of jumbled together Judge what matters by ABNG problems! Chapter 8: Pretty much self study, not many ABNGs, I don’t care about solubility (yawn) Chapter 9: MUCH harder; includes limiting Reagent… that’s the hardest it gets! We saw in the banana problem already, but now we have to figure it out! 1 Here’s what people said they learned. 2 Here’s what people said they wanted to know better. 3 Maybe this never happened; click the story for a link. Moral of this story •Do not smoke •Insecticides can ignite •Requires spark •Gives off energy •You have to be careful with chemistry Time to do REAL chemistry: Starting Chapter 8,9,10 now. 4 More Announcements Wednesday, March 27 Ch. 8,9 There will be a LOT of assigned problems here ….because it really matters. I don’t fuss much with “rules” of solubility—so many exceptions; however, it’s good to know all nitrates are soluble. I don’t care if a reaction is a decomposition or a displacement or a metathesis. No wonder people “despise” chemistry. 5 You already know some important things. Conservation of Numbers: in a chemical rxn, atoms aren't changed, lost or made. Same is true of electrons, protons & neutrons. Conservation of Mass: mass isn't gained or lost either (neglecting those tiny losses in nuclear reactions). Chemistry goes by integer numbers – very large integers. 7 Zillions of molecules or atoms are usually involved. C + O CO We think: one atom at a time. Reality: zillions of C’s, zillions of O’s, zillion’s of CO’s 8 Practice with sub-Zillion Numbers makes it easier for us….I hope. One dozen cookies = 12 cookies Two dozen eyes = 24 eyes Four dozen yellow frosting zones = = 48 squeezes of yellow frosting tube. Other convenient numbers: Baker’s dozen = 13 Gross = dozen dozen = 144 9 The mole is the chemist’s dozen. Avogadro's number = 602202035873921029561369 = 6.02202035873921029561369 x 1023 This is a lie!!!! 10 Atomic Mass Unit. Pay attention—this is where Avogadro's number comes from. •Earlier we said "Let one atom of H have 1 atomic mass unit" •Now, we have a problem, because H has 3 isotopes: •So.....we cannot use "hydrogen" as it usually exists (mixed isotopes) for our mass standard. •We must purify it. •Easier to purify carbon, so carbon became the mass standard: Atomic mass unit: 1 a.m.u. = 1/12th the mass of isotope A single atom of = 1.660 x 10-24 g. weighs 12 x 1.660 x 10-24 g. 11 Avogadro’s Number is the inverse of a.m.u. How many atoms of are in 12.000 grams of pure isotope Answer: (12.000 grams of 1 Atom ) 12 x 1.660 x 10-24 grams ( ) = 6.022 x 1023 atoms It’s the same as the number of atoms of hydrogen in one gram of hydrogen (assuming only the “normal” hydrogen isotope). It’s the same as the number of atoms of iodine in 126.90 gram of iodine (assuming the natural abundance of iodine isotopes) 12 Avogadro’s Number: Fixing that Lie. We said: 602202035873921029561369 6.02202035873921029561369 x 1023 We really only know the first few digits, so: 6.02214129 x 1023 It does not look like an integer, but it has the meaning of an integer, just as one dozen is an integer. Because matter is discrete, it comes in integer amounts. LARGE integers. 13 Properly speaking, Avogadro’s number is a conversion factor, not just a number. Number: 12 Conversion factor: 12 as in 12 doughnuts/dozen Rewrite this: 12/dozen Rewrite it again: 12 dozen-1 Number: 6.022 x 1023 Conversion factor: 6.022 x 1023 as in 6.022 x 1023 per mol Rewrite this: 6.022 x 1023 /dozen Rewrite it again: 12 dozen-1 14 Why did I lie about Avogadro Number? To emphasize that Avogadro’s number is an integer CONCEPT, just as a dozen or a gross are integer numbers. All the things we do with ordinary integer numbers we also do with Avogadro’s number. Compare the national debt, another “big” number known to its smallest “quantum” of matter, which is the penny. National debt as of October 31, 2011 $10,205,557,724,099.29 Your share: $32,654.52 Taxes per person for balanced budget: $14,000/year http://www.odec.ca/projects/2008/stan8e2/hatom.jpg 15 A tirade on the irrelevance of detail… Wouldn’t $ x 1012 be close enough? Your share: $3.3 x 104 = $33,000 16 Compound Formula and Molecular Weights follow the same basic prescription as atoms. Molecular weight: how many a.m.u. per molecule (same as how many grams per 6.022 x 1023 molecules) Use for molecules! Formula weight: how many a.m.u. per formula (same as how many grams per 6.022 x 1023 repeats of the formula) Use for compounds or molecules. 17 Get Molecular weight: Example #1 for Louisiana: CH4 Example #2 for Louisiana: benzene, C6H6 18 Get Formula weight for : Ba(HCO3)2 Ba: 137.327 H: 1.008 C: 12.011 O: 15.999 19 What % of Ba(HCO3)2 is made of carbon? Ba: 137.327 H: 1.008 C: 12.011 O: 15.999 20 How many carbon atoms in 7.8 grams of benzene, C6H6 How many hydrogen atoms? How many MOL of H atoms? 21 Question: Which is potentially worth more, in terms of silver it can produce? 1000 g of AgCl or..... 1000 g of AgI or..... 1000 g of Ag NO3 ? or..... 500 g of Ag2CO3 Atomic wts: Ag =108, I = 127, C = 12, O = 16 22 Let's do another, perhaps a bit harder. 1. 2. 3. 4. What is molecular mass of penicillin, C16H17N2O5SK What is mass of 0.45 mol of penicillin? How many C atoms in 19.5 g of penicillin? What percentage of penicillin, by weight, is oxygen? Actually, I don’t think this is pencillin—maybe a derivative. Dorothy Crowfoot Hodgkin, Nobel Prize 1964 23 Reactions are like recipes. CH4 + O2 CO2 + H2O Unbalanced: a list of ingredients & results CH4 + 2O2 CO2 + 2H2O Balanced: a correct recipe Wheels + Pedals + Handlebar Bicycle Unbalanced: a list of ingredients & results 2 Wheels + 2 Pedals + 1 Handlebar Bicycle Balanced: a correct recipe 24 Chemical Equivalence: d The d symbol defines the relation between two compounds according to the particular balanced chemical reaction being considered. It acts like a conversion factor! Consider: 2 KClO3 2 KCl + 3 O2 2 KClO3 d 2 KCl which is the same as: 1 KClO3 d 1 KCl This simply means that one KCl will be produced for every KClO3 present in this reaction (other reactions that produce KCl will be different). 25 More about Chemical Equivalence: d 2 KClO3 2 KCl + 3 O2 KClO3: 122.45 g/mol KCl: 74.45 g/mol O2: 32 g/mol 74.54 g of KCl d 122.45 g of KClO3 We can also write: 2 KClO3 d 3 O2 Or: 244.9 g KClO3 d 96 g O2 This means we get 96 g of oxygen for every 244.9 g of KClO3. 26 What do chemists really use? 27 Another question on the same theme: How much KClO3 will I need to produce 1 ton of O2? 29 Another Example (more complex, but also more fun....and a little depressing!) How many tons of CO2 are produced by burning 1000 gallons of gasoline? Assume density of gasoline is 0.692 g/ml and formula is C8H18. 30 Chemistry is Imperfect Problem #1. Many possible reaction paths. We wrote: CH4 + 2O2 CO2 + 2H2O But methane can also do this: CH4 + O2 CO + 2H2O The second reaction makes deadly carbon monoxide; the first produces only benign CO2 and H2O. 31 Imperfection happens. Problem #2. A second problem is that we may inefficiently isolate a product. •product can stick to glassware. •it can vaporize. •it can get dropped on floor. •it can stick to filter paper, etc. •it can re-react (e.g., isolating K compared to Fe) •Like gambling, there are many ways to lose! 32 Theory vs. Reality: We actually quantify the amount of imperfection. Theoretical Yield: what God would get. Percent Yield: what you would get compared to what God would get as a chemist, expressed as a percentage. 33 Example 1 involves production of iron from iron ore. If you had 2 tons of rust (Fe2O3) how many tons of iron could you get from it? 3 Fe2O3 2Fe + O 2 2 34 Let’s do it by percent! 35 Or you can do it the hard way. (Having learned conversions, might as well use them.) 36 Suppose your metal processing plant loses some iron and you only get 1.35 tons. % Yield = 100 x 1.35/1.40 = 96 % 37 Example 2 Soda lime glass is made from this reaction*: Na2CO3 + SiO2 Na2(SiO3) + CO2 If we collect 200 g of CO2 from 1000 g of sodium carbonate and unlimited amounts of SiO2, what percent yield is that? 38 Now it is time to talk about limits! Limiting reagent problems are the hardest of the whole course for many students, but you can do them! We saw one in the banana quiz, but it was “easy”. 39 You actually ARE used to problems just like this. Consider a car. 1965 Plymouth Barracuda’s weigh 3,000 pounds. Supply Limits. Suppose Supply Limits. How many tires per 9,000 pounds of Fishcar? Supply you had 17Limits. tires; what is the most number of and cars 3 If you have 17 tires Answer: 12 (not counting the spare)(8 cylinders). It’scan a V8 engine you make? motors, how many cars 12 If you have 51 pistons, youofblocks make? How many cubic can inches engineand displacement engine 29 tires, per 15,000 poundshow of Fishcar? many cars can you 5 x 273 = 1365 cubicmake? inches How many horsepower per 18,000 pounds of Fishcar? About 6 cars X 270 hp = 1620 hp 40 Sometimes people can do these in their heads—we are very used to limits!—but let’s dissect it and see how we do it. Here’s the question again: It’s a V8 engine (8 cylinders). you have 51 pistons, 12 engine blocks and 29 tires, how many cars can you make? Write balanced equation: 8 pistons + 1 block + 4 tires = 1 car Start: 51 12 29 0 coefficient: 51/8 12/1 29/4 =6.375 =12 =7.25 *Limit = lowest 41 If 9.85 (ABNG) Na reacts with H2 to make NaH. A reaction mixture contains 10.0 g Na and 0.0235 g H2. When the reaction is performed, the chemist gets 0.428 g of NaH. What is her percent yield? 42 43 Reactions do not go all the way. It’s not really A + B C + D It’s more like: A + B C + D At any one time: zillions of A’s zillions of B’s zillions of C’s zillions of D’s Reactions that “go” More zillions of C’s and D’s Reactions that don’t “go” Less zillions of C’s and D’s 44 Energy helps to determine whether reaction goes or not (it is not the ultimate determinant, though) Energy A+B C+D Time (“reaction progress”) 45 2 questions about reactions: how fast? how far? Energy How fast A+B C+D How far Time (“reaction progress”) 46 Things that affect how fast include: Temperature: rate as T Pressure: rate as P Concentration: rate as c Catalyst: rate Energy A+B C+D With catalyst: lowers energy of activation. http://en.wikipedia.org/wiki/Enzyme Time (“reaction progress”) Biocatalyst = Enzyme. Enzymes are important! 47 Things that affect how far Chemists and, especially, chemical engineers who try to manipulate equilibrium. Let me try to explain….. 48 Equilibrium It’s more like: A + B C + D zillions of A’s zillions of B’s zillions of C’s zillions of D’s The molecules know what balance they want between A, B, C and D. Problem is: we may not necessarily agree! Western cultures (and chemists of all cultures) try to manipulate equilibrium, as if it is our manifest destiny to do so! 49 One of your first encounters with equilibrium was physical equilibrium between gases & liquids & solids. The Hot Soup Problem (It’s alphabet soup—hence the letters). 50 Why is equilibrium such a foreign concept? Because we are used to fairly small numbers in our daily lives. There are things that go like equilibrium, though. Example: attentiveness of spectators at a football game. "Concession customers" "Active spectators" 51 Can we manipulate this? Yes, by realizing that the equation is not complete. Concession customers + Scoring Drive Active spectators + Hunger 52 We can characterize this equilibrium by a number, the “equilibrium” constant, that shows the ratio of “product” to “reactant”. concession customers 72303 K 18 watching game 4118 53 Limits to Equilibrium What happens if we run out of Tiger Dogs? What happens if the food lines are too long? What happens if the oceans run out of capacity to buffer all the CO2 we are producing? 54 Returning to the soup problem… Hot soup Cold soup + Heat released If we remove heat from the soup in the form of hot vapor, the system will try to make more heat in the space above the soup. When it does, we get more cold soup. Blowing on soup is manipulating equilibrium! Heat Energy + H2O(l) H2O(g) Equilibrium between water liquid and water vapor. 55 Le Chatelier’s principle Shift To Right Add reactants Remove Products Shift To Left Remove reactants Add Products 56 Spontaneity! Who decides what's equilibrium? Which way to equilibrium? Observation: often, the reactions that occur spontaneously release heat energy (exothermic). But not always! Some endothermic reactions also occur spontaneously. 57 Entropy Reactions (changes) occur if they increase the disorderliness of the universe. “Disorderliness" is called "entropy" No one knows why this law holds true. Like any law, it's the sum total of our EXPERIMENTAL observations. You actually take much of this for granted, whether you realize it or not, when you use time: Entropy is time's arrow. "Forward" in times means more disordered! 58