Chapter 3 & 4: Reactions Part 1

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Stella McBride
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Chapter 3 & 4: Reactions Part 1 Read: BLB 3.1 3.2; 4.2 4.

1 Chapter 3 & 4: Reactions Part 1 Read: BLB ; HW: BLB 3:1, 11a, b, e, 13 4:19, 24, 39, 49a, c, e, f, 51b, d Supplemental: Rxns:1, 2, 6 11 Know: Chapter 3 Reactions Combustion Decomposition Combination Balancing Equations Law of conservation of mass: matter cannot be lost in any chemical reaction Chapter 4 Reactions Exchange reactions (Metathesis) Formation of a precipitate Formation of a gas Formation of a weak or non-electrolyte (neutralization) Late drop deadline: Check out the grade calculator on the Chem110 website or on the Angel Lessons Tab Review chemical nomenclature (SCT #5) Memorize those strong acids & bases (BLB Table 4.2) Bonus deadline for Skill Check Test #10: Missed Exam 1, 2 or 3? Request a sign up form for the Make-up Exam: Covers material from all midterm Exams. You must sign up by completing the request form & giving it to me (download on web). L. S. Van Der Sluys Page 1 Reactions Part 1 L. S. Van Der Sluys Page 2 Reactions Part 1

2 Balancing Chemical Equations Ch Write the unbalanced molecular equation (molecules involved with correct molecular formulas) CH 4 + O 2! CO 2 + H 2 O 2. Balance the elements that occur in the fewest chemical formulas on each side. CH 4 + O 2! CO 2 + H 2 O focus on C first, then H, then O CH 4 + O 2! CO 2 + H 2 O Patterns of reactivity Know how to balance a chemical reaction 1. (Complete) Combustion reactions (Ch. 3.2) C 3 H 8 (g) + 5O 2 (g)! 3CO 2 (g) + 4H 2 O(g) 2. Combination reactions (Chapter 3) 2Mg(s) + O 2 (l)! 2MgO(s) 3. Decomposition reactions (Chapter 3) Check: Is it balanced? Add atoms on both sides of the equation. Use Trial and Error PbCO 3 (s)!pbo(s) + CO 2 (g) L. S. Van Der Sluys Page 3 Reactions Part 1 L. S. Van Der Sluys Page 4 Reactions Part 1

3 Patterns of reactivity Continued 4. Exchange reactions (Chapter 4) a. Precipitation Use these patterns of reactivity to write balanced reactions for: 1. The combustion of ethanol (CH 3 CH 2 OH) Pb(NO 3 ) 2 (aq) + 2KI(aq)! PbI 2 (s) " + 2KNO 3 (aq) b. Neutralization 2. The decomposition of lead carbonate (PbCO 3 ) NaOH(aq) + HCl(aq)! NaCl(aq) + H 2 O(l) c. Gas formation 3. The combination of nitrogen and hydrogen to form ammonia (NH 3 ) 2HCl(aq) + Na 2 S(aq)! H 2 S(g) # + 2NaCl(aq) 5. Single displacement reactions (Redox: Ch. 4) 4. The combination of hydrogen and oxygen to form...? 2Ca(s) + O 2 (g)! 2CaO(s) L. S. Van Der Sluys Page 5 Reactions Part 1 L. S. Van Der Sluys Page 6 Reactions Part 1

4 Exchange reactions (Double Displacement or Metathesis Rxn) Exchange positive ions to get products AD + XZ! AZ + XD Reactants: Pb(NO 3 ) 2 + KI Products:! PbI 2 + KNO 3 Now Balance the reaction: Pb(NO 3 ) 2 + KI! PbI 2 + KNO 3 Does anything observable happen? Do you have to do the reaction to know? SOLUBILITY RULES FOR COMMON IONIC COMPOUNDS IN WATER (based on experimental observations) 1. Almost all ammonium and alkali metal salts are soluble. 2. Most nitrates, acetates, chlorides, bromides, and sulfates are soluble. Exceptions: silver halides sulfates of Ca, Ba, Pb, Ag 3. Most sulfides, carbonates, phosphates and hydroxides are insoluble. Exceptions: alkali salts ammonium salts (See #1 above.) Note: if the solubility of a substance is <0.01M it is considered insoluble. L. S. Van Der Sluys Page 7 Reactions Part 1 L. S. Van Der Sluys Page 8 Reactions Part 1

5 Balancing Reactions: Example: Net Ionic Equation for a Precipitation Reaction Mix silver nitrate and sodium chloride. What happens? 1. write correct molecular formulas for products and reactants 2. determine the phase (aq, s, l or g) of products 3. determine spectator ions and net ionic rxn 4. balance the mass and charge on both sides 1. Molecular Equation: are any combinations insoluble? AgNO 3 + NaCl! AgCl + NaNO 3 2. Ionic Equation: break apart all SOLUBLE electrolytes *Spectator ions: what species don't change on either side of the arrow? 3. Net Ionic Equation: which species actually change and react? L. S. Van Der Sluys Page 9 Reactions Part 1 L. S. Van Der Sluys Page 10 Reactions Part 1

6 Metathesis Reactions Require a Driving Force Given reactants: exchange positive ions to get products Driving Forces Include Formation of: How do you know what is happening? How do you predict the phase of the products? Use a Net Ionic Equation Acid-Base Reactions (Neutralization reaction) Acid + base! salt + water Molecular Equation HNO 3 (aq) + KOH(aq)! KNO 3 (aq) + H 2 O Ionic Equation Spectator ions: Net Ionic Equation L. S. Van Der Sluys Page 11 Reactions Part 1 L. S. Van Der Sluys Page 12 Reactions Part 1

7 Hydrogen Ion Transfer Examples: What is the net ionic equation for the reaction between sodium hydroxide and acetic acid? Acids: proton donors Bases: proton acceptors What is the net ionic equation for the reaction between sodium chloride and potassium iodide? L. S. Van Der Sluys Page 13 Reactions Part 1 L. S. Van Der Sluys Page 14 Reactions Part 1

8 5.2 Mixing solutions of K 2 SO 4 (aq) and BaCl 2 (aq) produces an insoluble salt. Which of the following is the correct list of spectator ions for this reaction? 1. K +, SO 2-4, Ba 2+, Cl - 2. K + 2-, SO 4 3. K +, Cl - 4. Ba 2+, Cl - 5. Ba 2+ 2-, SO 4 L. S. Van Der Sluys Page 15 Reactions Part 1

Reactions. Chapter 3 Combustion Decomposition Combination. Chapter 4 Reactions. Exchange reactions (Metathesis) Formation of a precipitate

Reactions. Chapter 3 Combustion Decomposition Combination. Chapter 4 Reactions. Exchange reactions (Metathesis) Formation of a precipitate Reactions Chapter 3 Combustion Decomposition Combination Chapter 4 Reactions Exchange reactions (Metathesis) Formation of a precipitate Formation of a gas Formation of a week or nonelectrolyte Single Displacement