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Chapter 7

Chapter 7. What is a chemical reaction? Writing and balancing chemical equations Types of reactions Predicting products Net Ionic equations. What is a chemical reaction?. Way back in Ch. 1, we defined a chemical change as “a change where new substances are formed” OR

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Chapter 7

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  1. Chapter 7 • What is a chemical reaction? • Writing and balancing chemical equations • Types of reactions • Predicting products • Net Ionic equations

  2. What is a chemical reaction? • Way back in Ch. 1, we defined a chemical change as • “a change where new substances are formed” • OR • “a process where chemical ID/formulas are changed”

  3. Reactant(s) Product(s) What is a chemical reaction? • A chemical reaction is the process in which reactants react to form products. • Reactants are the starting substances. • Products are the final substances.

  4. Symbols Used in Equations • + Used to separate 2 reactants or 2 products

  5. Symbols Used in Equations • + Used to separate 2 reactants or 2 products • “Yields,” separates reactants from products

  6. Symbols Used in Equations • + Used to separate 2 reactants or 2 products • “Yields,” separates reactants from products • (s), (l), (g) Shows a react. or prod. is in the solid, • liquid, or gaseous state

  7. Symbols Used in Equations • + Used to separate 2 reactants or 2 products • “Yields,” separates reactants from products • (s), (l), (g) Shows a react. or prod. is in the solid, • liquid, or gaseous state • (aq) “Aqueous” a react. or prod. is dissolved in H2O

  8. Symbols Used in Equations • + Used to separate 2 reactants or 2 products • “Yields,” separates reactants from products • (s), (l), (g) Shows a react. or prod. is in the solid, • liquid, or gaseous state • (aq) “Aqueous” a react. or prod. is dissolved in H2O • or heat Heat is supplied to the reaction

  9. Symbols Used in Equations • + Used to separate 2 reactants or 2 products • “Yields,” separates reactants from products • (s), (l), (g) Shows a react. or prod. is in the solid, • liquid, or gaseous state • (aq) “Aqueous” a react. or prod. is dissolved in H2O • or heat Heat is supplied to the reaction • Pt A formula written above the arrow shows that • a catalyst is used to speed up the reaction.

  10. Catalysts • Catalysts are neither reactants nor products; rather, they just help to speed up a reaction. The catalyst is unchanged by the reaction.

  11. Types of Reactions • There are 5 we’re concerned with here: • 1. Combination/Synthesis • 2. Decomposition • 3. Single Replacement • 4. Double Replacement • 5. Combustion

  12. Types of Reactions • 1. Combination/Synthesis • Two reactants become one product. • A + B AB • The reactants could be element(s) or compound(s) • The product must be a compound.

  13. SO2 + H2O H2SO3 Al + S Al2S3 Cr + O2 Cr2O3 Examples of combination rxns: These, of course, may need balancing.

  14. Types of Reactions • 2. Decomposition • One reactant becomes two products. • CD C + D • The reactant must be a compound. • The products may be either elements or compounds.

  15. H2CO3 CO2 + H2O PbO Pb + O2 C6H12O6 C + O2 + H2 Examples of decomposition rxns: These, of course, may need balancing.

  16. Types of Reactions • 3. Single Replacement • It’s like a date gone bad: • One element gets “kicked out” of a compound by another element. • XY + Z XZ + Y • We find a compound and an element on both sides of the equation.

  17. MgCO3 + LiLi2CO3 + Mg CaCl2 + F2 CaF2 + Cl2 Examples of SR rxns: Note that a metal replaces a metal. Note that a nonmetal replaces a nonmetal.

  18. Types of Reactions • 4. Double Replacement • Like a dancefloor partner-switch: • The cations and anions of two ionic compounds exchange. • CA + BDCD + BA • We find two ionic compounds on each side of the equation.

  19. Na2CO3 + CaBr2 CaCO3 + NaBr Examples of DR rxns: It kinda reminds me of FOIL from math class: The outer ions (of reactants) end up together, and the inner ions end up together.

  20. CxHy(Oz) + O2 CO2 + H2O Types of Reactions • 5. Combustion • You’ll recognize this: A compound made of carbon, hydrogen, (and sometimes oxygen) reacts with O2, forming CO2 and H2O. Oxygen is ALWAYS a reactant in a combustion reaction.

  21. C2H4 + O2 CO2 + H2O CH3COOH + O2 CO2 + H2O Examples of combustion rxns: Balance ‘em & you’re good!

  22. Signs a chemical reaction has occurred • Again, think back to Ch. 1: • • Since new substances are formed; • • & the new substance(s) have different properties • • we can usually see/sense that a reaction has occurred.

  23. Signs a chemical reaction has occurred • 1. Color change • 2. Odor change • 3. Formation of a gas • 4. Formation of a precipitate • 5. Energy (temperature) change

  24. Signs a chemical reaction has occurred • 1. Color change • A color change shows the formation of a different substance

  25. Signs a chemical reaction has occurred • 1. Color change • 2. Odor change • A new/different odor is also a sign of a new substance having been formed.

  26. Signs a chemical reaction has occurred • 1. Color change • 2. Odor change • 3. Formation of a gas • Shows the production of a new substance

  27. Signs a chemical reaction has occurred • 1. Color change • 2. Odor change • 3. Formation of a gas • 4. Formation of a precipitate • Commonly seen in DR reactions, mixing aqueous reactants can result in a insoluble, solid product called a precipitate.

  28. Signs a chemical reaction has occurred • 1. Color change • 2. Odor change • 3. Formation of a gas • 4. Formation of a precipitate • 5. Energy (temperature) change • Chemical reactions either release or absorb energy as they occur. Not always obvious.

  29. Predicting Products • By looking at a given set of reactants, we can predict what products can be made. • We’ll learn how to write formulas for products of select combination, DR, SR, and combustion reactions.

  30. Predicting Products:Combination reactions • We learned in Ch. 5 how to write formulas for ionic compounds: Consider the charges of the ions involved, and put them together in the ratio that gives zero net charge. • We’ll do the same here.

  31. Predicting Products:Combination reactions • ID your reactants: A metal element and nonmetal element. These can only combine! • Figure out what charge ions they’ll make. We’ll limit ourselves to the “A groups,” Ag (always +1), Cd and Zn (always +2) • Write the (single) product to have zero net charge, using LCM of charges.

  32. Predicting Products:Combination reactions • Na + Cl2

  33. Predicting Products:Combination reactions • Na + Cl2 • 2 elements; have to combine. • Na makes +1 ion, Cl makes -1 ion

  34. Predicting Products:Combination reactions • Na + Cl2 NaCl • Product written correctly; now balance equation.

  35. Predicting Products:Combination reactions • 2 Na + Cl2 2 NaCl • Done!

  36. Predicting Products:Combination reactions • Try another: • K + O2

  37. Predicting Products:Combination reactions • Try another: • K + O2 • K+ , O-2 will make K2O

  38. Predicting Products:Combination reactions • Try another: • 4 K + O2 2 K2O

  39. Predicting Products:SR reactions • ID your reactants: An element and a compound • Figure out what element can be replaced. Metals can replace metals; nm’s replace nm • Consider whether the element can replace that element from the compound. (next slide) • If rxn will take place, write product as ionic compound (ratio for LCM/zero net charge) • Consider if element product is HOFBrINCl?

  40. Will SR reaction occur? Element Activity • The rule is this: A more active element will replace a less active element. • Nonmetal activity series: Use the periodic table. F > Cl > Br > I • This means that F will replace any other halogen; I cannot replace any other halogen. • Cl can replace Br or I; Br can replace I only.

  41. Will SR reaction occur? Element Activity • The rule is this: A more active element will replace a less active element. • Metal activity series: Use the activity series given to you. • A metal higher on the chart can replace any metal lower on the activity chart.

  42. Will SR reaction occur? Element Activity • What if the element trying to replace the other is lower in activity? • No reaction will occur. • Write “NR” to show no reaction will occur.

  43. Writing products for SR reactions • Once you’ve decided that a SR reaction will occur, • you just need to write product formulas. • • The new compound is ionic: Determine its formula by thinking about ion charges of cation/anion. • • The element that gets kicked out will exist as it naturally does as an element. HOFBrINCl elements are diatomic, others are just the atom.

  44. SR example • Write products for the following rxn. Write ‘NR’ if no reaction occurs. • AlBr3 + Cl2

  45. SR example • Write products for the following rxn. Write ‘NR’ if no reaction occurs. • AlBr3 + Cl2 • Cl is trying to replace Br (both are nonmetals).

  46. SR example • Write products for the following rxn. Write ‘NR’ if no reaction occurs. • AlBr3 + Cl2 • Cl is trying to replace Br (both are nonmetals). • Cl is higher in activity than Br, so it can replace Br.

  47. SR example • Write products for the following rxn. Write ‘NR’ if no reaction occurs. • AlBr3 + Cl2 • Cl makes -1 ions; Al makes a +3 ion. Product is AlCl3. • Br will be diatomic, it becomes Br2 when by itself.

  48. SR example • Write products for the following rxn. Write ‘NR’ if no reaction occurs. • AlBr3 + Cl2 AlCl3 + Br2 • Cl makes -1 ions; Al makes a +3 ion. Product is AlCl3. • Br will be diatomic, it becomes Br2 when by itself.

  49. SR example • Write products for the following rxn. Write ‘NR’ if no reaction occurs. • 2 AlBr3 + 3 Cl2 2 AlCl3 + 3 Br2 • Balance!

  50. Predicting Products:DR reactions • ID your reactants: Two IONIC compounds • ID the cation and anion from each compound • Consider whether the reaction will occur. (See next slide) • If rxn will take place, write products as ionic compounds (ratio for LCM/zero net charge) • If the reaction won’t occur; NR

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