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Chapter4
- 1. CHEM 103 Chemical ReactionsChapter4 • Molecular and formula weight • Moles • Balancing equations • Calculating mass relationships • Percent Yield • Predicting interactions between ions in solutions • Oxidation/ Reduction reactions • Heat of Reaction
- 2. Formula weightFormula weight isthe sum of the atomic weights in amu units of all atoms in a compound’s formula. It can be used for both ionic and molecular compounds. The term molecular weight means the same thing but it is used only for covalent compounds and is expressed as g/mol.
- 4. THE MOLE The ratioof grams to molecular mass is so useful that it was given a name “the molethe mole” 1 mol H atoms = 1 g of Hydrogen 1 mol O atoms = 16.00 g of Oxygen
- 5. 1 mol of“something” always has 6.022 x 1023 “things” 1 mol of Cl2 molecules = 6.022 x 1023 molecules of Cl2 1 mol of Cl atoms = 6.022 x 1023 atoms of Cl Therefore there are: 6.022 x 1023 Hatoms in 1 g H ; atomic mass H = 1 amu 6.022 x 1023 Oatoms in 16 g O; atomic mass O = 16 amu Note: 6.022 x 1023 is known as Avogadro’s number
- 6. How many atomsof copper are in a 1.5 mole sample of copper? 1. 2. 3. 4.
- 7. The molar mass,MM, in grams per mole, is numerically equal to the sum of the masses (in amu) of the atoms in the formula. Formula Sum of Atomic Masses Molar Mass, MM O 16.00 amu 16.00 g/mol O2 2(16.00 amu) = 32.00 amu 32.00 g/mol H2O 2(1.008 amu) + 16.00 amu = 18.02 amu 18.02 g/mol NaCl 22.99 amu + 35.45 amu = 58.44 amu 58.44 g/mol
- 8. What is themolar mass of SO3? 1. 48.07 amu 2. 48.07 g/mol 3. 80.07 amu 4. 80.07 g/mol
- 9. The subscripts ina formula represent the atom ratio and/or mole ratio in which the different elements are combined. 1 mol of H20 1 mol of C9H8O4 Contains: Contains: 2 mol of H 9 mol of C 1 mol of O 8 mol of H 4 mol of O
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- 11. Calculate the numberof moles of water in 36.0 g of water 36.0 g H2O 1.00 mol H2O 18.0 g H2O = 2.00 mol H 2Ox
- 12. Calculate the numberof moles of sodium ions, Na+ , in 5.63 g of sodium sulfate, Na2SO4 formula weight = 2(23.0) + 32.1 + 4(16.0) = 142.1 amu therefore, 1 mol of Na2SO4 = 142.1 g Na2SO4 there are two moles of Na+ ions per mole of Na2SO40.0396 mol Na2SO 4 2 mol Na + 1 mol Na2SO 4 =x 0.0792 mol Na + 5.63 g Na2SO4 x 1.00 mol Na2SO4 142.1 g Na2SO4 = 0.0396 mol Na2SO4
- 13. A tablet ofaspirin, C9H8O4, contains 0.360 g of aspirin. How many molecules of aspirin are present? 0.360 g aspirin x 1 mol aspirin 180.0 g aspirin = 0.00200 mol aspirin 0.00200 mole x 6.02 x 1023 molecules mole = 1.20 x 1021 molecules
- 14. 1. 2. 3. 4. Howmany molecules of Cl2 are in a 54 g sample?
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- 16. Balancing Equations – beginwith atoms that appear only in one compound on both sides; in this case carbon (C) – now balance hydrogens, – if an atom occurs as a free element, as for example O2, balance it last:
- 17. 1. 1 2. 2 3.3 4. 4 What is the coefficient in front of O2 when the following equation is balanced? CH4 (g) + O2 (g) → CO2 (g) + H2O (g)
- 20. Stoichiometry StoichiometryStoichiometry:: the studyof mass relationships in chemical reactions
- 21. How many gramsof nitrogen, N2, are required to produce 7.50 g of ammonia, NH3 x 28.0 g N2 1 mol N2 = 6.18 g N2 7.50 g NH 3 x 1 mol NH3 17.0 g NH3 x 1 mol N2 2 mol NH3
- 22. 1. 0.0043 g 2.2.3 g 3. 15 g 4. 7800 g How many grams of NaCl can be produced when 5.8 g Na reacts with excess chlorine? 2 Na (s) + Cl2 (g) → 2 NaCl (s)
- 23. How many gramseach of CO22 and NH33 are produced from 0.83 mol of urea?
- 24. IDENTIFYING LIMITING REACTANTS ANDTHEORETICAL YIELD a) Calculate the amount of product that would form if the first reactant were completely consumed. b) Do this for the second reactant. c) The smaller number produced from the two calculations above is the theoretical yield of product, and the reactant that produced it is the limiting reactant.
- 25. Determine the limitingreactant and theoretical yield for 2Sb(s) + 3I2(g) 2SbI3 (s) a) When 1.2 mol of Sb and 2.4 mol of I2 are mixed n SbI3 from Sb = 1.20 mol Sb x 2 mol SbI3 = 1.20 mol SbI3 2 mol Sb n SbI3 from I2 = 2.40 mol I2 x 2 mol SbI3 = 1.60 mol SbI3 3 mol I2 Sb is the limiting reactant Theoretical yield = 1.20 mol SbI3
- 26. Determine the limitingreactant and theoretical yield for 2Sb(s) + 3I2(g) 2SbI3 (s) b) When 1.20 g of Sb and 2.4 g of I2 are mixed mass of SbI3 from Sb = 1.20 g Sb x 1 mol Sb x 2 mol SbI 3 x 502.5 g SbI 3 = 4.95 g SbI3 121.8 g Sb 2 mol Sb 1 mol SbI3 mass of SbI3 from I2 = 2.40 g I2 x 1 mol I2 x 2 mol SbI3 x 502.5 g SbI3 = 3.17 g SbI3 253.8 g I2 3 mol I2 1 mol SbI3 Therefore I2 is the limiting reactant and 3.17 g is the theoretical yield
- 27. 1. 9.6 g 2.11.6 g 3. 15 g 4. 24 g If 5.8 g Na react with 5.8 g Cl2, how much NaCl can be produced? 2 Na (s) + Cl2 (g) → 2 NaCl (s)
- 28. Percent YieldPercent Yield Experimentalyield:Experimental yield: the actual mass of product formed in a chemical reaction. Theoretical yield:Theoretical yield: the mass of product that should form according to the stoichiometry of the balanced equation. Percent yieldPercent yield:: experimental yield divided by theoretical yield times 100. Percent yield = Actual yield Theoretical yield x 100
- 29. A reaction produces28.4 g of product. If the theoretical yield for this experiment was 35.0 g, what is the percent yield? 1. 0.811% 2. 1.23% 3. 81.1% 4. 123%
- 30. In general, ionsin solution react with each other when one of the following can happen: • Two ions form a compound that is insoluble in water. • Two ions react to form a gas that escapes from the reaction mixture as bubbles (sodium bicarbonate and hydrochloric acid). • An acid neutralizes a base (Chapter 9). • One of the ions can oxidize another (Section 5.7).
- 32. SOLUBILITY These are somegeneralizations : – All compounds containing Na+ , K+ , and NH4 + are soluble in water. – All nitrates (NO3 - ) and acetates (CH3COO- ) are soluble in water. – Most chlorides (Cl- ) and sulfates (SO4 2- ) are soluble in water; exceptions are AgCl, PbCl2, BaSO4, and PbSO4. – Most carbonates (CO3 2- ), phosphates (PO4 3- ), sulfides (S2- ), and hydroxides (OH- ) are insoluble in water; exceptions are LiOH, NaOH, KOH, and NH4OH, which are soluble in water.
- 33. We can simplifyby omitting all ions that do not participate in the reaction: The equation is called a net ionic equationnet ionic equation. Ions that do not participate in a reaction are called spectator ionsspectator ions..
- 34. OXIDATION-REDUCTION REACTIONS A commontype of reaction in aqueous solution involves transfer of electrons between two species. Such reactions are called redox reaction. In a redox reactions one species loses (donates) electrons and is said to be oxidized. This species is called the reducing agent. The other species gains electrons (receives) and is reduced. This species is named the oxidizing agent.
- 36. The net ionicequation is This equation can be split into two half-equations: Zn(s) Zn2+ (aq) + 2e- Zn is oxidized Cu2+ (aq) + 2e- Cu(s) Cu2+ is reduced Note that oxidation and reduction occur together and that there is no net change in the number of electrons in the reaction. Reducing agent Oxidizing agent
- 37. Oxidation:Oxidation: gain ofoxygen and/or loss of hydrogen. Reduction:Reduction: loss of oxygen and/or gain of hydrogen.
- 38. 1. oxidized; gaining 2.oxidized; losing 3. reduced; gaining 4. reduced; losing Aluminum is _______ because it is _______ electrons. Al(s) → Al 3+ (aq) + 3 e-
- 39. CombustionCombustion:: burning inair. The products of complete combustion of carbon compounds are CO2 and H2O. 2 C8H18 (l) + 25 O2 (g) 16 CO2 (g) + 18 H2O (l) + Heat Five important types of redox reactionsFive important types of redox reactions
- 40. Respiration:Respiration: the processby which living organisms oxidize carbon-containing compounds for energy.
- 41. RustingRusting:: the oxidationof iron to iron oxides
- 42. BleachingBleaching:: the oxidationof colored compounds to colorless products.
- 43. BatteriesBatteries:: in allcases, the reaction taking place in a battery is a redox-reaction.
- 44. Heat of Reaction Inalmost all chemical reactions, heat is either given off or absorbed plus 1263.1 kcal of heat
- 45. Heat of reaction:Heatof reaction: the heat given off or absorbed in a chemical reaction. exothermic reaction:exothermic reaction: one that gives off heat. endothermic reaction:endothermic reaction: one that absorbs heat.
Editor's Notes
- #9 Image question has &dash:
- #43 Sodium hypochlorite (NaOCl) or hydrogen peroxide (H2O2) are quite effective in "decolorizing" substances via oxidation The decolorizing action of bleaches is due in part to their ability to remove these electrons which are activated by visible light to produce the various colors. The hypochlorite ion (OCl-), is reduced to chloride ions and hydroxide ions forming a basic solution as it accepts electrons from the colored material as shown below. OCl- + 2e- + HOH --------> Cl- + 2 OH- http://library.kcc.hawaii.edu/external/chemistry/everyday_bleach.html
- #44 Anode Pb (s) + HSO4- (aq) PbSO4 (s) + H+ (aq) + 2 e- Catode PbO2 (s) + HSO4- (aq) + 3 H+ (aq) + 2 e- PbSO4 (s) + 2 H2O (l) REDOX: Pb (s) + PbO2 (s) + 2 HSO4- (aq) + 2 H+ (aq) 2 PbSO4 (s) + 2 H2O (l) Eo CELL = 2.0 volts (Car batteries have 6 such cells in series to give 6 x 2.0 volts = 12 volts)