Chemistry Notes Week 3
Chemistry Notes Week 3 CHE 105
Popular in Chemistry: Principles and Applications
Popular in Chemistry
This 4 page Class Notes was uploaded by Catherine Carter on Sunday September 18, 2016. The Class Notes belongs to CHE 105 at University at Buffalo taught by Melvyn Churchill in Summer 2015. Since its upload, it has received 2 views. For similar materials see Chemistry: Principles and Applications in Chemistry at University at Buffalo.
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Date Created: 09/18/16
law of the conservation of mass says that an equal amount of matter exists both before and after the experiment chemical equations are concise representations of chemical reactions o reactants are on the left side of the equation and products are on the right o the states of the substances (solid, liquid, or gas) may be written in parenthesis after the substance o coefficients are inserted before the substance to ensure that everything in the equation is balanced you can never change the subscript to balance an equation there are three types of reactions, combination, decomposition, and combustion o combination reactions are when two or more substances combine to form one product o decomposition reactions are when a single substance decomposes to produce two or more substances o combustion reactions are rapid reactions that produce a flame molecular weight or molecular mass is the sum of the atomic weights of all the atoms in the molecule in amu Formula weight (typically only done for ionic compounds) is the sum of the atomic weights of the atoms in the chemical formula the empirical formula weight is usually a lot less that a substance’s molecular weight to get the percent composition Avogadro’s number is the scale factor between amu and molar mass (grams) the number is 6.02x10^23 (6.02x10^23 amu = 1g) o there are 6.02x10^23 molecules or atoms in 1 mole o molar mass is the mass of exactly 1 mole of a substance (g/mol) the molar mass is numerically the same as its molecular or formula weight Atoms/ molecules mass Avagadro’s # molar mass Moles o how to derive the empirical formula from the percent composition: o the mole ratio is the subscript of each element o convert everything to moles ten divide each quantity by the thing with the smallest number of moles, this gets you the molar ratio o to go from empirical to molecular you have to divide the molecular mass by the mass of the empirical formula o these skills can be used to analyze combustion reactions and elements Coefficients in a balanced equation give the “mole ratio” of reactants and products o see the triangle for the route o limiting reactant/reagent limits how much product can be produced excess reactant/reagent is left over at the end of the reaction calculate the amount of product produced from each reactant, whichever one produces the lease amount of product is the limiting reactant o the theoretical yield is the maximum amount of product that can be made and is predicted using stoichiometry o the percent yield is found by solutions are homogenous mixtures of two or more pure substances the solvent is present in the greatest abundance, all other substances are solutes the dissociation and solvation of an ionic material o the water molecules pull the individual cations and anions from the crystal and solvate them o dissociation of the ionic material, solvation of the cations and anions o substances that dissociate into ions when dissolved in water behave as electrolytes because the charged cations and anions allow the solution to conduct electricity o soluble ionic compounds act as electrolytes nonelectrolytes may dissolve in water but they do not dissociate into ions and do not conduct electricity through the solution o molecular compounds tend to be nonelectrolytes (unless they are acids or bases or undergo hydrolysis in solution) a strong electrolyte dissociates completely when dissolved in water and readily conducts electricity, a weak electrolyte only dissociates partially when dissolved in water o strong electrolytes are strong acids, strong bases and soluble ionic salts o strong acids o strong bases o strong electrolytes o weak electrolytes: weak acids (acetic acid CH3CO2H), weak bases (ammonia NH3) both of which are only partially ionized, and nonelectrolytes such as molecular solids and liquids Metathesis Reactions (exchange reactions) involve exchanging ions in solution and will proceed in solution due to one of three driving forces: o formation of an insoluble solid (precipitate) o formation of a covalently bonded weak or nonelectrolyte o formation of an insoluble gas o metathesis comes from a greek word meaning “to transpose” and the ions in the reactant compounds exchange or “transpose” ions in order to understand reactivity you must know which species are changing during the reaction o the word equation just states the chemical names of the products and reactants o the molecular equation contains the chemical formulas for the products and reactants in their usual molecular form with phases o the complete ionic equations shows all strong electrolytes written in dissociated form, this reflects the species that are actually present in the reaction mixture (still includes the phases) o the net ionic equation shows only the things that change, you start with the complete ionic equation then cancel what is exactly the same on both the product and reactant sides then balance what is left over. What was canceled from the equation is known as the spectator ions, meaning they do not affect the reaction taking place, they’re simply there to write a net ionic equation you must first write the balanced molecular equation, then convert all strong electrolytes to their ions (complete ionic equation), then cross out those species that are unchanged from the reactants to the products, you then have the net ionic equation
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