Chem 101 1nd EditionExam # 2 Study Guide Lectures: 7 - 13Chapter 3: Chemical ReactionsLecture 7 (September 17)A chemical reaction involves a rearrangement and or a change in oxidation state of atoms (transfer of valence electrons) from reactants to products. Evidence of a chemical reaction includes gas evolution, temperature or color change, and precipitation. An example for how to describe a chemical reaction is as follows: Reactants: Zn(s) +I2(s) Products: ZnI2(s) (Zinc Iodide) + (energy). It is important to have a balanced chemical equation because of the Law of Conversion of Matter which states that matter can neither be created nor destroyed.Consider this example: 4 Al(s) + 3 O2(g) 2Al2O3(s). The leading numbers (4, 3 and 2) are called stoichiometric coefficients and they represent how many moles of Al (in this example) we need to react with how ever many moles of O2 to make 2 moles of 2Al2O3. So in this example, 4 moles of Al + 3 moles of O2 react to form 2 moles of 2Al2O3.Chemical Equilibrium: Reactants Products N2(g) + 3H2(g) 2NH3(g)Consider the reverse reaction (with a double arrow): N2(g) + 3H2(g) 2NH3(g). once an equilibrium is achieved, the reaction continues, but there is no net change in the amounts of products or reactants. Chemical reactions always proceed spontaneously toward equilibrium. Once an equilibrium is established, we can recognize if the reaction is product-favored (after the reaction is over, there are more products than reactants) or reactant favored (after the reaction is over, there are more reactants than products).A solution is the substance which is dissolved (the smaller amount), and the solvent is the substance that dissolves (the larger amount). Water is always the solvent in aqueous solutions. Compounds whose aqueous solutions conduct electricity are called electrolytes (ions in a solution). All ionic compounds that are water-soluble, are also electrolytes. 1. A strong electrolyte is an ion with a high number of charged particles and it completely dissociates in a solution. These electrolytes show a strong tendency to dissociate and conduct electricity well. (HCl(aq) CuCl2(aq) and NaCl(aq)) 2. A weak electrolyte is an ion with a low number of charged particles and very little of it is dissociated in a solution. These exist in solution under equilibrium conditions and they conduct electricity poorly. The molecular form is preferred in the solution.3. A non-electrolyte is an ion where there are no charged particles and very little to no dissociation in a solution. They dissolve in water, but don’t conduct electricity (sugar, ethanol, ethylene glycol)Lecture 8 (September 24)When ions are present in water, the solutions conduct electricity. Soluble ionic compounds include:1. Salts of Na^(+), K^(+), NH4^(+)2. Salts of NO3^(-), ClO3^(-), ClO4^(-)3. Salts of Halides, X^(-)4. Salts of SO4^(2-)Exceptions include 1. Halides of Ag^(+), Hg2^(2+), Pb^(2+), MgF2, CaF2, SrF2, BaF2, PbF22. Earth Alkalines: CaSO4, SrSO4, BaSO4, PbSO4, Ag2SO4*MEMORIZEInsoluble ionic compounds include:1. Salts of CO3^(2-), PO4^(3-), (COO)2^(2-) (oxalate), CrO4^(2-) (chromate), S^(2-), O^(2-), OH^(-)Exceptions include:1. Salts of NH4^(+) and alkali metal ions2. Alkali metal hydroxides Ba(OH)2, Sr(OH)2In class experiment example: When equal amounts of aqueous solutions of 0.1 M calcium acetate and 0.1 M potassium carbonate are mixed together, a precipitate forms. (1 M= 1 mol/L; unit of concentration of a solution). When they were added together, they did not mix, but instead formed precipitate which looked like clouds. There was a higher concentration at the top and a lower concentration at the bottom, meaning we had to add more of the potassium carbonate to “mix” it more and make it more even.Ca(Ac)2(aq) + K2CO3(aq) 2K(Ac)(aq) + CaCO3 (s) *the downward arrow is common to represent the precipitate in the formulathe Complete Ionic Reaction would be:Ca^(2+)(aq) + 2Ac^(-)(aq) + 2 K^(+)(aq) + CO3^(2-) (aq) 2K^(+)(aq) + 2Ac^(-)(aq) + CaCO3 (s)The Net Ionic Equation would beCa^(2+)(aq) + 2Ac^(-)(aq) + 2 K^(+)(aq) + CO3^(2-) (aq) 2K^(+)(aq) + 2Ac^(-)(aq) + CaCO3 (s)Ca^(2+)(aq) + CO3^(2-)(aq) CaCO3 (s)The Arrhenius Definition: An acid is any substance that increases the H^(+)(aq) concentration in an aqueous solutionHX(aq) H^(+)(aq) + X^(-)(aq)A base is any substance that increases the OH^(-)(aq) concentration in an aqueous solution. MOH(aq)M^(+)(aq) +OH^(-)(aq)The Brønsted-Lowry Definition:An acid is any substance that donates H^(+) to another species in an aqueous solution.HX(aq) + H2O(l) H3O^(+)(aq) + X^(-)(aq)A base is any substance that accepts H^(+) in an aqueous solutionH3O^(+)(aq) + NH3(aq) NH4^(+)(aq)Strong acids = strong electrolytes Weak acids = weak electrolytesStrong bases = strong electrolytes Weak bases = weak electrolytesAmphiprotic compound is a compound hat is able to function as a base and an acid. Reaction between strong acids and strong bases: NeutralizationOverall reaction:HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)Complete Ionic Equation:H3O^(+)(aq) + Cl^(-)(aq) + Na^(+)(aq) + OH^(-)(aq) 2 H2O(l) + Na^(+)(aq) + Cl^(-)Net Ionic Equation:H3O^(+)(aq) + OH^(-)(aq) 2H2O(l)Reaction between weak acids and strong bases:Overall Reaction:HAc(aq) + NaOH(aq) H2O(l) + NaAc(aq)Complete Ionic Equation:HAc(aq) + Na^(+)(aq) + OH^(-)(aq)H2O(l) + Na^(+)(aq) Ac^(-)(aq)Net Ionic Equation:HAc(aq) + OH^(-)(aq)H2O(l) + Ac^(-)(aq)Reaction between weak acids and strong bases:Net Ionic Equation:HAc(aq) + OH(aq) H2O(l) + Ac^(-)(aq)The Resulting Solution is Basic:Ac^(-)(aq) + H2O(l) HAc(aq) + OH^(-)(aq)(reverse/competing reaction of the equilibrium)Reaction between strong acids and weak bases:Overall Reaction:HCl(aq) + NH3(aq) NH4Cl(aq)Complete Ionic Equation:H3O^(+)(aq) + Cl^(-)(aq) + NH3 (aq) H2O(l) + NH4^(+)(aq) + Cl^(-)(aq)Net Ionic Equation:H3O^(+)(aq) + NH3(aq) H2O(l) + NH4^(+)(aq)The Resulting Solution is Acidic:NH4^(+)(aq) + H2O(l) NH3 (aq) +H3O^(+)(aq)(reverse/competing reaction of the equilibrium)Oxides of nonmetals such as CO2, SO2, SO3, and NO2 are called acidic oxides since they react to acids with waterCO2(g) +H2O(l) H2CO3(aq)SO2(g) + H2O(l) HSO3(aq)SO3(g) + H2O(l) HSO4(aq)2NO2(g) + H2O(l) HNO3(aq) + HNO2(aq)Lecture 9 (September 26)Oxides of
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