Slide 1Chemical FormulasSlide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Chemical Reactions & EquationsSlide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Chemical StoichiometrySlide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Limiting Reactants and Product YieldsSlide 37Slide 38Slide 39Product YieldsSlide 41Slide 42Slide 43Slide 44Chemical FormulasMethaneCH4MOLECULAR FORMULAS: representation of molecules in terms of their constituent atoms -– H2, H2ODIATOMIC - two atoms; example: H2, N2, CO (carbon monoxide)TRIATOMIC - three atoms; example: CO2 (carbon dioxide), O3(ozone)POLYATOMIC - more than three atoms; examples: NH3 (ammonia), CH4 (methane), C2H6O2 (ethylene glycol)What limits the “boundary” of a molecule?Atoms in molecules are held together by strong interactions called CHEMICAL BONDSInteractions between neutral atoms in a molecule (e.g. H2, H2O) is called a COVALENT bond, forming covalent compoundsInteractions between charged elements (IONS) result in a different kind of chemical bond, called an IONIC BONDCompounds formed via interactions between ionic (charged) elements are called ionic compounds.In a crystal of NaCl a Na+ ion interacts with the neighboring Cl- ion, hence a NaCl “molecule” does not exist.However, if one counted the number of sodium ions and the number of Cl- ions in a given volume we would find that the ratio of Na+ : Cl- is 1:1. A crystal of sodium chloride is electrically neutral and its CHEMICAL FORMULA can be expressed as NaCl.Chemical formulas indicate the constituent elements in a compound (covalent or ionic)The term molecular formula refers specifically to covalent compounds.How are chemical formulas determined?ELEMENTAL ANALYSISDetermination of the relative amounts of the elements in a compoundDetermines the EMPIRICAL FORMULA which is the simplest possible formula and indicates the relative amounts of constituent elementsFor example, the molecular formula of hydrogen peroxide is H2O2; its empirical formula is HO.The empirical and the chemical formula can be the same, for example, H2O.For ionic compounds, the empirical formula is the same as the chemical formula (NaCl)ProblemAn oxide of nitrogen is analyzed and found to contain 25.9% N and 74.1% O. What is the empirical formula of the compound?In 100.0 g of compound:# moles of N = 25.9 g N / (14.01 g/mol) = 1.85 mol# moles of O = 74.1 g O / (16.00 g/mol) = 4.63 molRatio of O: N :: 2.5:1Must be whole numbers – N2O5Combustion Analysis - elemental analysis of organic compounds.Organic compounds contain predominantly C and H.Minor elements include O, N, S, Cl, P, etc.In combustion analysis the organic compound is burnt in the presence of oxygen (O2) to form carbon dioxide (CO2), water (H2O) and other gases (nitrogen (N2), sulfur dioxide (SO2))A sample of a compound that is known to contain only carbon, hydrogen, and oxygen is combusted, and the CO2 and H2O produced are trapped and weighed. The original sample weighed 8.38 g and yielded 16.0 g CO2 and 9.5 g H2O. What is the empirical formula?Need to determine the number of moles of C and H in the compound, and then determine the mass of O in the compound.Moles of C = (16.0 g CO2 / 44.0 g/mol CO2) x (1 mol C/1 mol CO2) = 0.364 mol CMoles of H =(9.80 g H2O / 18.0 g/mol H2O) x (2 mol H / 1 mol H2O)= 1.09 mol HMass of C in compound = 0.364 mol C x 12.0 g/mol C = 4.37 g CMass of H in compound = 1.09 mol H x 1.01 g/ mol H = 1.10 g HMass of O in compound = 8.38 g - 4.37 g - 1.10 g = 2.91 g OMoles of O in compound = (2.91 g O / 16.0 g/mol O) = 0.182 mol OMole ratio of C : H : O is 0.364 : 1.09 : 0.182 or 2:6:1Hence empirical formula is C2H6ODetermining Chemical FormulasThe empirical formula tells you the simplest ratio of the individual elements in the compound. For an ionic compound this information is enough. For a molecular compound this may not be enough since the empirical formula may not be the molecular formula. Knowledge of the MOLAR MASS of the compound and its empirical formula, allows the molecular formula to be determined.Elemental analysis of a sugar shows that it consists of 40.0% carbon (C), 6.7% hydrogen (H), 53.3% oxygen (O). The molar mass of the compound was found to be 180.0 g/mol. What is the molecular formula of the compound?moles of C in 100.0 g of compound = (mass of C g)/(atomic mass g/mol) = 40.0/12.01 = 3.33 mol C in 100.0 g of compoundmoles of H in 100.0 g of compound = (mass of H g)/(atomic mass g/mol)= 6.7/1.01 = 6.7 mol H in 100.0 g of compoundmoles of O in 100.0 g of compound = (mass of O g)/(atomic mass g/mol)= 53.3/16.00 = 3.33 mol O in 100.0 g of compoundRatio of C:H:O :: 1:2:1; hence empirical formula is CH2OMolar mass of empirical formula = 12.01 + 2(1.01) + 16.00 = 30.0 g/molRatio of molar mass of compound : molar mass of empirical formula180.0/30.0 = 6.0molecular formula is (CH2O) 6 or C6H12O6Chemical Reactions & EquationsIn a chemical reaction elements and/or compounds collide, interact and react to form new compounds. The compounds that come together are called the REACTANTS and the new compounds formed are the PRODUCTS.An important aspect of a chemical reaction is that MASS IS ALWAYS CONSERVED - i.e. the total mass of the reactants must equal the total mass of the products.To ensure that mass is conserved, we have to keep track of the number of atoms of each element in the reactants and number of atoms of each element in the productsWriting Chemical EquationsreactantsH2 + O2  H2OproductsMass has not been conserved - equation is not BALANCEDNeed to make sure that the number of atoms of a given element is the same on either side.H2 + O2  H2OH is balanced, but O is not.To balance O, multiply H2O by 2H2 + O2  2 H2ONow O is balanced but not H (4 H’s on right, 2 on left)Multiply H2 by 22H2 + O2  2 H2ONow the equation is balanced.However, for a complete chemical equation the state of all reactants and products must be included2H2 + O2  2 H2O2H2(g) + O2 (g)  2 H2O (g) g - gas; l - liquid; s- solidaq - denotes a solution of a solute in water (solvent)Note: the subscripts in the molecular formula must never be changed in balancing equations. Changing the subscript corresponds to a different molecular formula, hence a different molecule, with completely different properties“Rules” to balance chemical equationsConsider the reaction of methane, CH4, burning in air to produce CO2 and H2O