Ch. 3 Chemical Reactions and Reaction Stoichiometry- Stoichiometry: Area of study that examines quantities of substances consumed and produced in chemical reactions- Law of conservation of masso Foundation of stoichiometryo Antoine Lavoisier in 1700so Atoms are neither created nor destroyed during a chemical reaction.3.1 Chemical Equations-Chemical equations: Represent chemical reactions-+ means “reacts with” and arrow means “produces”-Reactants: Left of arrow, starting substances-Products: Right of arrow, substances produced in reaction-Coefficients: Relative numbers of molecules of each kind-Balanced: Equal number of atoms of each element on each side of equation-Number of atoms is obtained by multiplying each subscript in chemical formula by coefficient for the formula.Balancing Equations:-Smallest possible number whole-number coefficients-Never change subscripts when balancing an equation.-Placing a coefficient in front of formula, changes only amount not identity.-Balance elements that occur in the fewest chemical formulas of equation first.Indicating the States of Reactants and Products:-Symbols (g), (l), (s), and (aq)-Sometimes symbols representing conditions under which reaction proceeds appear above or below reaction arrow3.2 Simple Patterns of Chemical ReactivityCombination and Decomposition Reactions:-Combination reactions: Two or more substances react to form one product.o Combination reaction between metal and nonmetal produces ionic solid.oA + B→C-Decomposition reactions: A single reactant breaks apart to form two or more substances.oC → A +Bo Ex. Decomposition of CaCO3 by heating to produce CaO and CO2o Ex. Sodium azide (NaN3) inflates safety air bags by release of nitrogen gas by decompositionCombustion Reactions:-Combustion reactions: Rapid reactions that produce a flame-Hydrocarbons combusted in air react with O2 to form CO2 and H2O.o Whether water is gas or liquid depends on reaction conditions; H2O(g) forms at high temp. in an open container-Oxygen-containing derivatives of hydrocarbons also produce CO2 and H2O.-Reactions with intermediate steps described as oxidation reactions3.3 Formula Weights-Chemical formulas and equations have a quantitative significance in that subscripts and coefficients represent precise quantities.Formula and Molecular Weights:- Formula weight (FW): Sum of the atomic weights (AW) of atoms in the chemical formula of substance- Molecular weight (MW): Another name for formula weight when dealing with a molecule- Ionic substances can’t be referred to as molecules because ions exist as 3-D arrays of ions.Percentage Composition from Chemical Formulas:- Percentage composition (elemental composition): Percentage mass contributed by each element in the substanceo3.4 Avogadro’s Number and the Mole- Mole: Amount of matter that contains as many objects (atoms, molecules, etc.) as number of atoms in 12 g of isotopically pure 12C.- Avogadro’s number (NA): Amount of objects (atoms, molecules, etc.) in one mole of substanceo 6.022 x 1023- Ex. Molar Mass:- 1-mol samples of different substances have different masses.- The atomic weight of an element in atomic mass units is numerically equal to the mass in grams of 1 mol (molar mass) of that element.- Molar mass: Mass in grams of one mol of a substanceInterconverting Masses and Moles:- Molar mass provides factor for converting grams to moles or moles to grams.Interconverting Masses and Numbers of Particles:- Molar mass and Avogadro’s number used as conversion factors to convert grams to moles and then moles to atoms.- Calculate number of atoms typically very large3.5 Empirical Formulas from Analyses- Ratio of numbers of moles of all elements in a compound gives the subscripts in the smpd’s empirical formula.- Ex. - Subscripts of empirical formula are smallest integers that express ratio of atoms present in cmpd.Molecular Formulas from Empirical Formulas:- Obtain molecular formula of cmpd from empirical formula if molecular weight or molar mass of cmpd is known- Subscripts in molecular formula of substance are always whole-number multiples of subscripts inempirical formula.-Whole− number multiple=molecular weightempirical formula weightCombustion Analysis:- Dimensional analysis to change mass of CO2 to mass of C, and mass of H2O to mass of H- Mass of sample subtracted by mass of C and H produces mass of O- All masses converted to moles, divided by smallest amount of moles to find relative numbers of moles3.6 Quantitative Information from Balanced Equations- The coefficients in a balanced chemical equation indicate both relative numbers of molecules (or formula units) in reaction and relative numbers of moles.- : stoichiometrically equivalent to-3.7 Limiting Reactants- Limiting reactant: Reactant completely consumed in reaction, which determines amount of product formed- Excess reactant: Reactant that is present in larger amounts that limiting reactantTheoretical and Percent Yields:- Theoretical yield: Quantity of product calculated to form when all of a limiting reactant is consumed- Actual yield: Amount of product actually obtained in a reactiono Almost always less than theoretical yield- Percent yield: Relates actual and theoretical