CHAPTER 6 – CHEMICAL REACTIONS 5A-1 (of 34) 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

CHEMICAL EQUATION – A representation of a chemical reaction using elemental symbols and chemical formulas Hydrogen gas and oxygen gas produce water when sparked H 2 + O 2 → H 2 O ↑ “Yields” REACTANTS – Sustances on the left PRODUCTS – Substances on the right In a chemical reaction, atoms are neither created nor destroyed All atoms of the reactants must be accounted for in the products Satisfying this is called BALANCING THE EQUATION 5A-2

H 2 + O 2 → H 2 O 2 -H O - 1 5A-3

H 2 + O 2 → H 2 O 2 -H O A-4

H 2 + O 2 → H 2 O 2 -H O Chemical equations are balanced by adjusting the coefficients, not by changing the formulas of any reactant or product 5A-5

Physical states of reactants and products can be represented by (s)solid (l)liquid (g)gas (aq)dissolved in water 2Na (s) + 2H 2 O (l) → 2NaOH (aq) + H 2 (g) 5A-6

BALANCING CHEMICAL EQUATIONS Mg + HCl → MgCl 2 + H 2 1 -Mg H Cl A-7

HgO → Hg + O 2 1 -Hg O A-8

KClO 3 → KCl + O 2 1 -K Cl O HINT: When the atoms of an element are odd and even, adjust each to a common multiple 5A-9

CH 4 + O 2 → CO 2 + H 2 O 1 -C H O HINT: Balance the element that appears in the most substances last 5A-10

NH 3 + O 2 → NO + H 2 O 1 -N H O ½ 5 NH 3 + O 2 → NO + H 2 O A-11 HINT: To remove fractional coefficients, multiply all coefficients by the denominator of the fraction

C 2 H 6 + O 2 → CO 2 + H 2 O 5A-12

Fe(NO 3 ) 3 + NaOH → Fe(OH) 3 + NaNO 3 1 -Fe NO Na OH HINT: If a polyatomic ion is a reactant and a product, balance it as a single element 3 5A-13

K 2 SO 4 + Ba(C 2 H 3 O 2 ) 2 → KC 2 H 3 O 2 + BaSO 4 5A-14

H 3 PO 4 + LiOH → Li 3 PO 4 + H 2 O HINT: Water can be written as H(OH) to balance the hydrogens and hydroxides separately H2OH2O 5A-15

H 3 PO 4 + LiOH → Li 3 PO H PO Li OH HINT: Water can be written as H(OH) to balance the hydrogens and hydroxides separately 3 H(OH)HOH 3 3 5A-16

Na + H 2 O → NaOH + H 2 H2OH2O 5A-17

Na + → NaOH + H 2 H(OH) 1 -Na H OH- 1 HOH A-18

CHAPTER 7b – CLASSIFICATIONS OF CHEMICAL REACTIONS (A)Oxidation-Reduction Reactions (1)Composition (2)Decomposition (3)Replacement (4)Combustion (B)Exchange Reactions (5)Precipitation (6)Acid-Base 5A-19

OXIDATION-REDUCTION REACTION – One that transfers electrons from one atom to another Also called a REDOX REACTION (1)Composition Reactions Mg + S → ( A + B → AB ) MgS A-20

Mg → Mg e - OXIDATION – Losing electrons 2e - + S → S 2- REDUCTION – Gaining electrons LEO says GER Metals and nonmetals react to form ionic compounds by transferring e - s form metal to nonmetal 5A-21

Sodium metal reacts with chlorine gas Na + Cl 2 →NaCl2 2(s) (g)(s) Aluminum metal reacts with fluorine gas 5A-22

(2)Decomposition Reactions( AB → A + B ) Mercury (II) oxide is heated HgO →Hg + O 2 22(s)(l)(g) Electricity is passed through molten sodium chloride 5A-23

(3)Replacement Reactions( A + BX → AX + B ) Magnesium metal is heated with iron (III) oxide Mg +Fe 2 O 3 →MgO + Fe23(s) No Reaction Iron is heated with magnesium oxide Replacement reactions occur when the elemental reactant (A) is more active than the element in the compound (B) 3(s) Active elemental metals react with less active metal ions 5A-24

Chlorine gas is bubbled through a sodium bromide solution Cl 2 + NaBr →NaCl + Br 2 22(g)(aq) (l) Active elemental nonmetals react with less active nonmetal ions No Reaction Liquid bromine is poured into a sodium chloride solution 5A-25

Zinc metal reacts with hydrochloric acid Zn + HCl →ZnCl 2 + H 2 2(s)(aq) (g) Most metals (except the Noble Metals) will react with the hydrogen ions from acids Copper metal reacts with hydrochloric acid No Reaction 5A-26

Sodium metal reacts with water Na + H 2 O → Alkali metals (and Alkaline Earth metals below Mg) will react with the hydrogen from water 5A-27

Sodium metal reacts with water Na + →NaOH + H (s) (aq) (g) 2H(OH) Alkali metals (and Alkaline Earth metals below Mg) will react with the hydrogen from water 5A-28

(4)Combustion Reactions( AB + O 2 → AO + BO ) Methane burns in air CH 4 + O 2 →CO 2 + H 2 O2 2(g) Combustion or burning means REACTS WITH OXYGEN (g) Combustion makes oxide compounds of each element in the compound burned 5A-29

Octane (C 8 H 18 ) burns in air C 8 H 18 + O 2 → CO 2 + H 2 O9 12½ 8 C 8 H 18 + O 2 → CO 2 + H 2 O18 25 (l) (g) 162 5A-30

Octane (C 8 H 18 ) burns in air C 8 H 18 + O 2 → CO 2 + H 2 O9 12½ 8 C 8 H 18 + O 2 → CO 2 + H 2 O18 25 (l) (g) 162 5A-30

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 5A-31

Solutions of lead (II) nitrate and sodium iodide are mixed Pb(NO 3 ) 2 + NaI → PbI 2 + NaNO 3 22(aq) (s)(aq) Solutions of barium chloride and potassium sulfate are mixed 5A-32

(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 + NaOH → HOH + NaCl(aq) (l)(aq) Solutions of sulfuric acid and potassium hydroxide are mixed 5A-33