CHAPTER 6 CHEMICAL REACTIONS EVIDENCE FOR CHEMICAL CHANGE

CHAPTER 6 – CHEMICAL REACTIONS EVIDENCE FOR CHEMICAL CHANGE 1) Color change 2) A solid forms 3) Bubbles are formed 4) A flame is produces 5) Heat is absorbed or released 5 A-1 (of 34) (15 – 26 -32 + 1 -13) (16 – 14 -23) (17 – 24 -27 + 1 -19)

CHEMICAL EQUATION – A representation of a chemical reaction using elemental symbols and chemical formulas Zinc metal reacts with hydrochloric acid Zn + 5 A-2 HCl → H 2 + ?

CHEMICAL EQUATION – A representation of a chemical reaction using elemental symbols and chemical formulas Zinc metal reacts with hydrochloric acid Zn + HCl → H 2 ↑ “Yields” + Zn. Cl 2 In a chemical reaction, atoms are neither created nor destroyed REACTANTS – Substances on the left PRODUCTS – Substances on the right 5 A-3

Hydrogen gas and oxygen gas produce water when sparked H 2 + O 2 → H 2 O 2 - H - 2 2 - O - 1 All atoms of the reactants must be accounted for in the products Satisfying this is called BALANCING THE EQUATION 5 A-4

Hydrogen gas and oxygen gas produce water when sparked H 2 + O 2 → H 2 O 2 2 - H - 2 2 - O - 1 All atoms of the reactants must be accounted for in the products Satisfying this is called BALANCING THE EQUATION 5 A-5

Hydrogen gas and oxygen gas produce water when sparked 2 H 2 + O 2 → 2 H 2 O 4 2 - H - 2 4 2 - O - 1 2 All atoms of the reactants must be accounted for in the products Satisfying this is called BALANCING THE EQUATION Chemical equations are balanced by adjusting the COEFFICIENTS, not by changing the formulas of any reactant or product 5 A-6

BALANCING CHEMICAL EQUATIONS 2 KCl. O 3 → 2 KCl + 3 O 2 2 1 - K - 1 2 2 1 - Cl - 1 2 6 3 - O - 2 6 HINT: When the atoms of an element are odd and even, adjust each to a common multiple 5 A-7

CH 4 + 2 O 2 → CO 2 + 2 H 2 O 1 - C- 1 4 - H- 2 4 4 2 - O- 3 4 HINT: Balance the element that appears in the most substances LAST 5 A-8

2 NH 3 + 2½ O 2 → 2 NO + 3 H 2 O 2 1 - N- 1 2 6 3 - H- 2 6 5 2 - O- 2 4 5 4 NH 3 + 5 O 2 → 4 NO + 6 H 2 O HINT: To remove fractional coefficients, multiply all coefficients by the denominator of the fraction 5 A-9

Fe(NO 3)3 + 3 Na. OH 1 3 3 1 → - Fe - NO 3 - Na - OH Fe(OH)3 - + 3 Na. NO 3 1 1 3 3 HINT: If a polyatomic ion is a reactant AND a product, balance it as a single element 5 A-10

H 3 PO 4 + Li. OH → Li 3 PO 4 + H 2 O HINT: Water can be written as H(OH) to balance the hydrogens and hydroxides separately 5 A-11

H 3 PO 4 + 3 Li. OH OH 3 1 3 1 → Li 3 PO 4 + 3 H(OH) OH - 1 3 - PO 4 - 1 - Li - 3 - OH - 1 3 HINT: Water can be written as H(OH) to balance the hydrogens and hydroxides separately 5 A-12

Physical states of reactants and products can be represented by (s) (l) (g) (aq) solid liquid gas dissolved in water 2 Na (s) + 2 H 2 O (l) → 2 Na. OH (aq) + H 2 (g) 5 A-13

CHAPTER 7 b – CLASSIFICATIONS OF CHEMICAL REACTIONS (A) Oxidation-Reduction Reactions (1) Composition (2) Decomposition (3) Replacement (4) Combustion (B) Exchange Reactions (5) Precipitation (6) Acid-Base 5 A-14

OXIDATION-REDUCTION REACTION – One that transfers electrons from one atom to another Also called a REDOX REACTION ( A + B → AB ) Composition Reactions (1) Two elements change electrons and combine to form one compound Mg 5 A-15 + S → Mg. S 2+ 2 -

Mg → Mg 2+ + 2 e- OXIDATION – Losing electrons 2 e- + S → S 2 - REDUCTION – Gaining electrons Metals and nonmetals react to form ionic compounds by transferring e-s from metal to nonmetal 5 A-16 LEO says GER

Sodium metal reacts with chlorine gas 2 Na (s) + Cl 2 (g) → Oxidation: Reduction: 2 e- + 2 Na. Cl (s) 2 Na → 2 Na+ Cl 2 → 2 Cl- + 2 e- Aluminum metal reacts with fluorine gas 2 Al (s) + 3 F 2 (g) → 2 Al. F 3 (s) 2 Al → 2 Al 3+ 3 F 2 → 6 F- Oxidation: Reduction: 5 A-17 6 e- + + 6 e-

(2) Decomposition Reactions ( AB → A + B ) One compound breaks down into elements when they exchange electrons Mercury (II) oxide is heated 2 Hg. O (s) → 2 Hg (l) + O 2 (g) Electricity is passed through molten sodium chloride 2 Na. Cl (l) 5 A-18 → 2 Na (s) + Cl 2 (g)

(3) Replacement Reactions ( A + BX → AX + B ) Replacement reactions occur when a more active element (A) changes electrons with a less active ion (B) in a compound (a) Active elemental metals react with less active metal ions Magnesium metal is heated with iron (III) oxide 3 Mg (s) + Fe 2 O 3 (s) → 3 Mg. O (s) + 2 Fe (s) Iron is heated with magnesium oxide Fe 5 A-19 + Mg. O → No Reaction

(b) Active elemental nonmetals react with less active nonmetal ions Chlorine gas is bubbled through a sodium bromide solution Cl 2 (g) + 5 A-20 2 Na. Br (aq) → 2 Na. Cl (aq) + Br 2 (l)

(c) Most metals (except the Noble Metals) will react with the hydrogen ions from acids Zinc metal reacts with hydrochloric acid Zn (s) + 2 HCl (aq) → Zn. Cl 2 (aq) + Copper metal reacts with hydrochloric acid Cu 5 A-21 + HCl → No Reaction H 2 (g)

(d) Alkali metals (and Alkaline Earth metals below Mg) will react with the hydrogen from water Sodium metal reacts with water Na 5 A-22 + H 2 O →

(d) Alkali metals (and Alkaline Earth metals below Mg) will react with the hydrogen from water Sodium metal reacts with water 2 Na (s) + 5 A-23 2 H(OH) (l) → 2 Na. OH (aq) + H 2 (g)

(4) Combustion Reactions ( AB + O 2 → AO + BO ) Combustion or burning means REACTS WITH OXYGEN Combustion makes oxide compounds of each element in the compound burned 5 A-24

Octane (C 8 H 18) burns in air C 8 H 18 + 12½ O 2 2 C 8 H 18 (l) + 5 A-25 → 25 O 2 (g) → 8 CO 2 + 9 H 2 O 16 CO 2 (g) + 18 H 2 O (g)

EXCHANGE REACTION – One in which ions in two compounds rearrange their bonding (5) Precipitation Reactions ( AX + BY → AY + BX ) Ions in solution rearrange to produce an insoluble product PRECIPITATE – A solid formed when two solutions are mixed 5 A-26

Solutions of lead (II) nitrate and sodium iodide are mixed Pb(NO 3)2 (aq) + 5 A-27 2 Na. I (aq) → Pb. I 2 (s) + 2 Na. NO 3 (aq)

(6) Acid-Base Reactions ( HX + AOH → HOH + AX ) Ions in solution rearrange to produce water Solutions of hydrochloric acid and sodium hydroxide are mixed HCl (aq) + Na. OH (aq) → H(OH) (l) + Na. Cl (aq) Solutions of sulfuric acid and potassium hydroxide are mixed H 2 SO 4 (aq) + 5 A-27 2 KOH (aq) → 2 H(OH) (l) + K 2 SO 4 (aq)