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Chapter 5 Chemical Reactions and Quantities Type of Reactions 5.3 Types of Reactions Chemical reactions can be classified as § Combination reactions. § Decomposition reactions. § Single Replacement reactions. § Double Replacement reactions. 1 Combination 2 Formation of MgO In a combination reaction, § Two or more elements (or simple compounds) combine to form one product A + B A B 2Mg(s) + O2(g) 2MgO(s) 2Na(s) + Cl2(g) 2NaCl(s) SO3(g) + H2O(l) H2SO4(aq) 3 Decomposition 4 Decomposition of HgO In a decomposition reaction, § One substance splits into two or more simpler substances. 2HgO(s) 2Hg(l) + O2(g) 2KClO3(s) 2KCl(s) + 3O2(g) 5 6 1 Learning Check Single Replacement In a single replacement reaction, § One element takes the place of a different element in a reacting compound. Classify the following reactions as 1) combination or 2) decomposition: ___A. H2(g) + Br2(g) 2HBr(l) ___B. Al2(CO3)3(s) Al2O3(s) + 3CO2(g) ___C. 4Al(s) + 3C(s) Al4C3(s) Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g) Fe(s) + CuSO4(aq) FeSO4(aq) + Cu(s) 7 Zn and HCl is a Single Replacement Reaction 8 Double Replacement In a double replacement, § Two elements in the reactants exchange places. AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq) ZnS(s) ZnCl2(aq) + H2S(g) + 2HCl(aq) 9 Example of a Double Replacement 10 Learning Check Classify the following reactions as 1) single replacement 2) double replacement 11 A. 2Al(s) + 3H2SO4(aq) Al2(SO4)3(s) + 3H2(g) B. Na2SO4(aq) + 2AgNO3(aq) Ag2SO4(s) + 2NaNO3(aq) C. 3C(s) + Fe2O3(s) 2Fe(s) + 3CO(g) 12 2 Chapter 5 Chemical Reactions and Quantities Learning Check Identify each reaction as 1) combination 3) single replacement A. B. C. D. E. 3Ba(s) + N2(g) 2Ag(s) + H2S(aq) SiO2(s) + 4HF(aq) PbCl2(aq) + K2SO4(aq) K2CO3(s) 5.4 Oxidation-Reduction Reactions 2) decomposition 4) double replacement Ba3N2(s) Ag2S(s) + H2(g) SiF4(s) + 2H2O(l) 2KCl(aq) + PbSO4(s) K2O(aq) + CO2(g) 13 Oxidation and Reduction 14 Electron Loss and Gain An oxidation-reduction reaction An oxidation-reduction reaction § Provides us with energy from food. § Provides electrical energy in batteries. § Occurs when iron rusts. 4Fe(s) + 3O2(g) 2Fe2O3(s) § Transfers electrons from one reactant to another. A Loss of Electrons is Oxidation Zn(s) Zn2+(aq) + 2e- (LEO) A Gain of Electrons is Reduction Cu2+(aq) + 2eCu(s) (GER) 15 16 Zn and Cu2+ Oxidation and Reduction oxidation Zn(s) Silvery metal Zn2+(aq) + 2ereduction Cu2+(aq) + 2eBlue 17 Cu(s) orange 18 3 Electron Transfer from Zn to Cu2+ Learning Check Identify each of the following as 1) oxidation or 2) reduction: Oxidation: electron loss __A. Sn(s) Sn4+(aq) + 4e− __B. Fe3+(aq) + 1e− Fe2+(aq) __C. Cl2(g) + 2e− 2Cl-(aq) Reduction: electron gain 19 Writing Oxidation and Reduction Reactions Learning Check Write the separate oxidation and reduction reactions for the following equation. 2Cs(s) + F2(g) In light-sensitive sunglasses, UV light initiates an oxidation-reduction reaction. uv light Ag+ + Cl− Ag + Cl 2CsF(s) Each cesium atom loses an electron to form cesium ion. 2Cs(s) 2Cs+(s) + 2e− 20 A. Which reactant is oxidized? oxidation B. Which reactant is reduced? Fluorine atoms gain electrons to form fluoride ions. F2(s) + 2e- 2F−(s) reduction 21 Learning Check Identify the substances that are oxidized and reduced in each of the following reactions: A. Mg(s) + 2H+(aq) Mg2+(aq) + H2(g) B. 2Al(s) + 3Br2(g) 2AlBr3(s) 22 TYPES OF CHEMICAL REACTIONS • Chemical reactions are often classified into categories according to characteristics of the reactions. The following is a useful classification scheme: 23 4 Chapter 5 Chemical Reactions and Quantities Collection Terms A collection term states a specific number of items. 5.5 The Mole § 1 dozen donuts = 12 donuts § 1 ream of paper = 500 sheets § 1 case = 24 cans 25 A Mole of Atoms A Mole of a Compound A mole A mole is a collection that contains § Of a covalent compound has Avogadro s number of § The same number of particles as there are carbon atoms in 12.0 g of carbon 26 molecules. 12C. § 6.02 x 1023 atoms of an element (Avogadro s number). 1 mole element Number of Atoms 1 mole C = 6.02 x 1023 C atoms 1 mole Na = 6.02 x 1023 1 mole Au = 6.02 x 1023 Au atoms 1 mole CO2 = 6.02 x 1023 CO2 molecules 1 mole H2O = 6.02 x 1023 H2O molecules § Of an ionic compound contains Avogadro s number of formula units. Na atoms 1 mole NaCl = 6.02 x 1023 NaCl formula units 1 mole K2SO4 = 6.02 x 1023 K2SO4 formula units 27 Particle in One-Mole Samples 28 Avogadro s Number Avogadro s number 6.02 x 1023 can be written as an TABLE 5.3 equality and two conversion factors. Equality: 1 mole = 6.02 x 1023 particles Conversion Factors: 6.02 x 1023 particles 1 mole 29 and 1 mole 6.02 x 1023 particles 30 5 Using Avogadro s Number Using Avogadro s Number Avogadro s number is used to convert moles of a substance to particles. Avogadro s number is used to convert particles of a substance to moles. How many Cu atoms are in How many moles of CO2 are in 2.50 x 1024 molecules CO2? 0.50 mole Cu? 2.50 x 1024 molecules CO2 x 0.50 mole Cu x 6.02 x 1023 Cu atoms 1 mole Cu = 3.0 x 1023 Cu atoms 1 mole CO2 6.02 x 1023 molecules CO2 = 4.15 moles CO2 31 32 Learning Check Subscripts and Moles 1. The number of atoms in 2.0 moles Al is The subscripts in a formula give § The relationship of atoms in the formula. § The moles of each element in 1 mole of compound. A. 2.0 Al atoms B. 3.0 x 1023 Al atoms C. 1.2 x 1024 Al atoms Glucose C6H12O6 2. The number of moles of S in 1.8 x 1024 atoms S is A. 1.0 mole S atoms In 1 molecule: 6 atoms C 12 atoms H 6 atoms O In 1 mole: 6 moles C 12 moles H 6 moles O B. 3.0 moles S atoms C. 1.1 x 1048 moles S atoms 33 Subscripts State Atoms and Moles 34 Factors from Subscripts Subscripts used for conversion factors § Relate moles of each element in 1 mole compound. § For aspirin C9H8O4 can be written as: 9 moles C 1 mole C9H8O4 8 moles H 1 mole C9H8O4 4 moles O 1 mole C9H8O4 1 mole C9H8O4 8 moles H 1 mole C9H8O4 4 moles O and 1 mole C9H8O4 9 moles C 1 mole C9H8O4 = 9 moles C 8 moles H 4 moles O 35 36 6 Learning Check 5.6 Molar Mass A. How many moles O are in 0.150 mole aspirin C9H8O4? The molar mass is § The mass of one mole of a substance. § The atomic mass of an element expressed in grams. B. How many O atoms are in 0.150 mole aspirin C9H8O4? 37 Learning Check 38 Molar Mass of CaCl2 Give the molar mass to the nearest 0.1 g. A. K = ________ B. Sn = ________ § For a compound, the molar mass is the sum of the molar masses of the elements in the formula. We calculate the molar mass of CaCl2 to the nearest 0.1 g as follows. Element Number of Moles Atomic Mass Total Mass Ca 1 40.1 g/mole 40.1 g Cl 2 35.5 g/mole 71.0 g CaCl2 111.1 g 39 Molar Mass of K3PO4 Learning Check Calculate the molar mass to the nearest 0.1g Determine the molar mass of K3PO4 to 0.1 g. A. K2O = Element Number of Moles Atomic Mass K 3 39.1 g/mole 117.3 g P 1 31.0 g/mole 31.0 g O 4 16.0 g/mole K3PO4 40 ______ g Total Mass in K3PO4 B. Al(OH)3 = ______ g 64.0 g 212.3 g 41 42 7 Conversion Factors from Molar Mass Learning Check Prozac, C17H18F3NO, is an antidepressant that inhibits the uptake of serotonin by the brain. What is the molar mass of Prozac? 1) 40.0 g/mole Methane CH4 known as natural gas is used in gas cook tops and gas heaters. 1 mole CH4 = 2) 262 g/mole 16.0 g The molar mass of methane can be written as conversion factors. 16.0 g CH4 and 1 mole CH4 1 mole CH4 16.0 g CH4 3) 309 g/mole 43 Learning Check 44 Calculations Using Molar Mass Acetic acid C2H4O2 gives the sour taste to vinegar. Write two molar mass conversion factors for acetic acid. § Mole factors are used to convert between the grams of a substance and the number of moles. Grams Mole factor Moles 45 Calculating Grams from Moles Learning Check Aluminum is often used for the structure of lightweight bicycle frames. How many grams of Al are in 3.00 moles of Al? 3.00 moles Al x 27.0 g Al 1 mole Al 46 The artificial sweetener aspartame (Nutri-Sweet) C14H18N2O5 is used to sweeten diet foods, coffee and soft drinks. How many moles of aspartame are present in 225 g of aspartame? = 81.0 g Al mole factor for Al 47 48 8