Chapter 5 Chemical Quantities and Reactions. Collection Terms. 5.1 The Mole. A Mole of a Compound. A Mole of Atoms.

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1 Chapter 5 Chemical Quantities and Reactions 5.1 The Mole Collection Terms A collection term states a specific number of items. 1 dozen donuts = 12 donuts 1 ream of paper = 500 sheets 1 case = 24 cans 1 2 A Mole of Atoms A Mole of a Compound A mole is a collection that contains the same number of particles as there are carbon atoms in 12.0 g of carbon x atoms of an element (Avogadro s number). 1 mole element Number of Atoms 1 mole C = 6.02 x C atoms 1 mole Na = 6.02 x Na atoms 1 mole Au = 6.02 x Au atoms A mole of a covalent compound has Avogadro s number of molecules. 1 mole CO 2 = 6.02 x CO 2 molecules 1 mole H 2 O = 6.02 x H 2 O molecules of an ionic compound contains Avogadro s number of formula units. 1 mole NaCl = 6.02 x NaCl formula units 1 mole K 2 SO 4 = 6.02 x K 2 SO 4 formula units 3 4 Samples of 1 Mole Quantities Avogadro s Number 1 mole of C atoms = 6.02 x C atoms 1 mole of Al atoms = 6.02 x Al atoms 1 mole of S atoms = 6.02 x S atoms 1 mole of H 2 O molecules = 6.02 x H 2 O molecules 1 mole of CCl 4 molecules = 6.02 x CCl 4 molecules Avogadro s number, 6.02 x 10 23, can be written as an equality and two conversion factors. Equality: 1 mole = 6.02 x particles Conversion Factors: 6.02 x particles and 1 mole 1 mole 6.02 x particles 5 6

2 Using Avogadro s Number Converting Moles to Particles Avogadro s number is used to o convert moles to particles o convert particles to moles Avogadro s number is used to convert moles of a substance to particles. How many Cu atoms are in 0.50 mole of Cu? 0.50 mole Cu x 6.02 x Cu atoms 1 mole Cu = 3.0 x Cu atoms 7 8 Converting Particles to Moles Avogadro s number is used to convert particles of a substance to moles. How many moles of CO 2 are in 2.50 x molecules CO 2? 2.50 x molecules CO 2 x 1 mole CO x molecules CO 2 = 4.15 moles of CO 2 1. The number of atoms in 2.0 mole of Al atoms is A. 2.0 Al atoms. B. 3.0 x Al atoms. C. 1.2 x Al atoms. 2. The number of moles of S in 1.8 x atoms of S is A. 1.0 mole of S atoms. B. 3.0 moles of S atoms. C. 1.1 x moles of S atoms Subscripts and Moles C. 1.2 x Al atoms 2.0 mole Al x 6.02 x Al atoms = 1 mole Al B. 3.0 moles of S atoms 1.8 x S atoms x 1 mole S = 6.02 x S atoms The subscripts in a formula show the relationship of atoms in the formula. the moles of each element in 1 mole of compound. Glucose C 6 H 12 O 6 In 1 molecule: 6 atoms C 12 atoms H 6 atoms O In 1 mole: 6 moles C 12 moles H 6 moles O 11 12

3 Subscripts State Atoms and Moles Factors from Subscripts The subscripts are used to write conversion factors for moles of each element in 1 mole of a compound. For aspirin, C 9 H 8 O 4, the possible conversion factors are: 9 moles C 8 moles H 4 moles O 1 mole C 9 H 8 O 4 1 mole C 9 H 8 O 4 1 mole C 9 H 8 O 4 and 9 moles of C 8 moles of H 4 moles of O 1 mole C 9 H 8 O 4 1 mole C 9 H 8 O 4 1 mole C 9 H 8 O 4 9 moles C 8 moles H 4 moles O A. How many moles of O are in mole of aspirin, C 9 H 8 O 4? B. How many atoms of O are in mole of aspirin, C 9 H 8 O 4? A. Moles of O in mole of aspirin, C 9 H 8 O mole C 9 H 8 O 4 x 4 mole O = mole of O 1 mole C 9 H 8 O 4 subscript factor B. Atoms of O in mole of aspirin, C 9 H 8 O mole C 9 H 8 O 4 x 4 mole O x 6.02 x O atoms 1 mole C 9 H 8 O 4 1 mole O Avogadro s number = 3.61 x atoms of O Chapter 5 Chemical Quantities and Reactions 5.2 Molar Mass Molar Mass The molar mass is the mass of 1 mole of an element or compound. is the atomic or molecular mass expressed in grams

4 Molar Mass from Periodic Table Molar mass is the atomic mass expressed in grams. Give the molar mass for each (to the tenths decimal place). A. 1 mole of K atoms = B. 1 mole of Sn atoms = 1 mole of Ag 1 mole of C 1 mole of S = g = g = g Guide to Calculation Molar Mass of a Compound Give the molar mass for each (to the tenths decimal place). A. 1 mole of K atoms = 39.1 g B. 1 mole of Sn atoms = g Molar Mass of a Compound Molar Mass of K 3 PO 4 The molar mass of a compound is the sum of the molar masses of the elements in the formula. Example: Calculate the molar mass of CaCl 2. Element Number Atomic Mass Total Mass of Moles Ca g/mole 40.1 g Cl g/mole 71.0 g CaCl g Calculate the molar mass of K 3 PO 4. Element Number of Moles Atomic Mass Total Mass in K 3 PO 4 K g/mole g P g/mole 31.0 g O g/mole 64.0 g K 3 PO g 23 24

5 Some 1-mole Quantities One-Mole Quantities What is the molar mass of each of the following? A. K 2 O B. Al(OH) g 55.9 g 58.5 g g g A. K 2 O 94.2 g/mole 2 moles of K (39.1 g/mole) + 1 mole of O (16.0 g/mole) 78.2 g g = 94.2 g B. Al(OH) g/mole 1 mole of Al (27.0 g/mole) + 3 moles of O (16.0 g/mole) + 3 moles of H (1.01 g/mole) 27.0 g g g = 78.0 g Prozac, C 17 H 18 F 3 NO, is an antidepressant that inhibits the uptake of serotonin by the brain. What is the molar mass of Prozac? 1) 40.1 g/mole 2) 262 g/mole 3) 309 g/mole Molar Mass Factors Prozac, C 17 H 18 F 3 NO, is an antidepressant that inhibits the uptake of serotonin by the brain. What is the molar mass of Prozac? 3) 309 g/mole 17 C (12.0) + 18 H (1.01) + 3 F (19.0) + 1 N (14.0) + 1 O (16.0) = 204 g C g H g F g N g O = 309 g/mole Molar mass conversion factors are fractions (ratios) written from the molar mass. relate grams and moles of an element or compound. for methane, CH 4, used in gas stoves and gas heaters is 1 mole of CH 4 = 16.0 g (molar mass equality) Conversion factors: 16.0 g CH 4 and 1 mole CH 4 1 mole CH g CH

6 Acetic acid, C 2 H 4 O 2, gives the sour taste to vinegar. Write two molar mass conversion factors for acetic acid. Calculate molar mass for acetic acid C 2 H 4 O 2 : 24.0 g C g H g O = 60.0 g/mole C 2 H 4 O 2 1 mole of acetic acid = 60.0 g acetic acid Molar mass factors: 1 mole acetic acid and 60.0 g acetic acid 60.0 g acetic acid 1 mole acetic acid Calculations Using Molar Mass Moles to Grams Molar mass factors are used to convert between the grams of a substance and the number of moles. Aluminum is often used to build lightweight bicycle frames. How many grams of Al are in 3.00 mole of Al? Molar mass equality: 1 mole of Al = 27.0 g of Al Grams Molar mass factor Moles Setup with molar mass as a factor: 3.00 mole Al x 27.0 g Al = 81.0 g of Al 1 mole Al molar mass factor for Al Grams, Moles, and Particles Calculate the molar mass of C 6 H 10 S. (6 x 12.0) + (10 x 1.01) + (1 x 32.1) = g/mole A molar mass factor and Avogadro s number convert Set up the calculation using a mole factor. 225 g C 6 H 10 S x 1 mole C 6 H 10 S g C 6 H 10 S molar mass factor (inverted) = 1.97 moles of C 6 H 10 S 35 36

7 How many H 2 O molecules are in 24.0 g of H 2 O? 1) 4.52 x H 2 O molecules 2) 1.44 x H 2 O molecules 3) 8.03 x H 2 O molecules How many H 2 O molecules are in 24.0 g of H 2 O? 3) 8.02 x g H 2 O x 1 mole H 2 O x 6.02 x H 2 O molecules 18.0 g H 2 O 1 mole H 2 O = 8.03 x H 2 O molecules If the odor of C 6 H 10 S can be detected from 2 x g in 1 liter of air, how many molecules of C 6 H 10 S are present? If the odor of C 6 H 10 S can be detected from 2 x g in 1 liter of air, how many molecules of C 6 H 10 S are present? 2 x g x 1 mole x 6.02 x molecules g 1 mole = 1 x 10 9 molecules of C 6 H 10 S are present If the odor of C 6 H 10 S can be detected from 2 x g in 1 liter of air, how many molecules of C 6 H 10 S are present? Chapter 5 Chemical Quantities and Reactions 5.3 Chemical Changes 2 x g x 1 mole x 6.02 x molecules g 1 mole = 1 x 10 9 molecules of C 6 H 10 S are present 41 42

8 Physical Change Chemical Change In a physical change, the state, shape, or size of the material changes. the identity and composition of the substance do not change. In a chemical change, reacting substances form new substances with different compositions and properties. a chemical reaction takes place Some Examples of Chemical and Physical Changes Classify each of the following as a 1) physical change or 2) chemical change. A. Burning a candle. B. Ice melting on the street. C. Toasting a marshmallow. D. Cutting a pizza. E. Polishing a silver bowl Chemical Reaction Classify each of the following as a 1) physical change or 2) chemical change. A. 2 Burning a candle. B. 1 Ice melting on the street. C. 2 Toasting a marshmallow. D. 1 Cutting a pizza. E. 2 Polishing a silver bowl. In a chemical reaction a chemical change produces one or more new substances. there is a change in the composition of one or more substances

9 Chemical Reaction Chemical Reaction In a chemical reaction old bonds are broken and new bonds are formed. atoms in the reactants are rearranged to form one or more different substances. In a chemical reaction the reactants are Fe and O 2. the new product Fe 2 O 3 is called rust Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Chemical Equations A chemical equation gives the formulas of the reactants on the left of the arrow. the formulas of the products on the right of the arrow. Reactants Product C(s) O 2 (g) CO 2 (g) Symbols Used in Equations Chemical Equations are Balanced Symbols in chemical equations show the states of the reactants. the states of the products. the reaction conditions. TABLE In a balanced chemical reaction no atoms are lost or gained. the number of reacting atoms is equal to the number of product atoms

10 A Balanced Chemical Equation In a balanced chemical equation, the number of each type of atom on the reactant side is equal to the number of each type of atom on the product side. numbers called coefficients are used in front of one or more formulas to balance the number of atoms. Al + S Al 2 S 3 Not Balanced 2Al + 3S Al 2 S 3 Balanced using coefficients 2 Al = 2 Al Equal number of Al atoms 3 S = 3 S Equal number of S atoms A Study Tip: Using Coefficients When balancing a chemical equation, use one or more coefficients to balance atoms. never change the subscripts of any formula. N 2 + O 2 NO Not Balanced N 2 + O 2 N 2 O 2 Incorrect formula N 2 + O 2 2NO Correctly balanced using coefficients State the number of atoms of each element on the reactant side and the product side for each of the following balanced equations. A. P 4 (s) + 6Br 2 (l) 4PBr 3 (g) B. 2Al(s) + Fe 2 O 3 (s) 2Fe(s) + Al 2 O 3 (s) A. P 4 (s) + 6Br 2 (l) 4PBr 3 (g) 4 P atoms = 4 P atoms 12 Br atoms = 12 Br atoms B. 2Al(s) + Fe 2 O 3 (s) 2Fe(s) + Al 2 O 3 (s) 2 Al atoms = 2 Al atoms 2 Fe atoms = 2 Fe atoms 3 O atoms = 3 O atoms Determine if each equation is balanced or not. A. Na(s) + N 2 (g) Na 3 N(s) B. C 2 H 4 (g) + H 2 O(l) C 2 H 6 O(l) Determine if each equation is balanced or not. A. Na(s) + N 2 (g) Na 3 N(s) No. 2 N atoms on reactant side; only 1 N atom on the product side. 1 Na atom on reactant side; 3 Na atoms on the product side. B. C 2 H 4 (g) + H 2 O(l) C 2 H 6 O(l) Yes. 2 C atoms = 2 C atoms 6 H atoms = 6 H atoms 1 O atom = 1 O atom 59 60

11 Guide to Balancing a Chemical Equation Steps in Balancing an Equation To balance the following equation, Fe 3 O 4 (s) + H 2 (g) Fe(s) + H 2 O(l) work on one element at a time. use only coefficients in front of formulas. do not change any subscripts. Fe: Fe 3 O 4 (s) + H 2 (g) 3Fe(s) + H 2 O(l) O: Fe 3 O 4 (s) + H 2 (g) 3Fe(s) + 4H 2 O(l) H: Fe 3 O 4 (s) + 4H 2 (g) 3Fe(s) + 4H 2 O(l) Balancing Chemical Equations 1. Write the equation with the correct formulas. NH 3 (g) + O 2 (g) NO(g) + H 2 O(g) 2. Determine if the equation is balanced. No, H atoms are not balanced. 3. Balance with coefficients in front of formulas. 2NH 3 (g) + O 2 (g) 2NO(g) + 3H 2 O(g) Double the coefficients to give even number of O atoms. 4NH 3 (g) + 7O 2 (g) 4NO(g) + 6H 2 O(g) Balancing Chemical Equations 4. Check that atoms of each element are equal in reactants and products. 4NH 3 (g) + 5O 2 (g) 4NO(g) + 6H 2 O(g) 4 N (4 x 1 N) = 4 N (4 x 1 N) 12 H (4 x 3 H) = 12 H (6 x 2 H) 10 O (5 x 2 O) = 10 O (4 O + 6 O) Equation for a Chemical Reaction Checking a Balanced Equation Reactants Products 1 C atom = 1 C atom 4 H atoms = 4 H atoms 4 O atoms = 4 O atoms 65 66

12 Check the balance of atoms in the following: Fe 3 O 4 (s) + 4H 2 (g) 3Fe(s) + 4H 2 O(l) A. Number of H atoms in products. 1) 2 2) 4 3) 8 B. Number of O atoms in reactants. 1) 2 2) 4 3) 8 C. Number of Fe atoms in reactants. 1) 1 2) 3 3) 4 Fe 3 O 4 (s) + 4H 2 (g) 3Fe(s) + 4H 2 O(l) A. Number of H atoms in products. 3) 8 (4H 2 O) B. Number of O atoms in reactants. 2) 4 (Fe 3 O 4 ) C. Number of Fe atoms in reactants. 2) 3 (Fe 3 O 4 ) Balance each equation and list the coefficients in the balanced equation going from reactants to products: A. Mg(s) + N 2 (g) Mg 3 N 2 (s) 1) 1, 3, 2 2) 3, 1, 2 3) 3, 1, 1 A. 3) 3, 1, 1 3Mg(s) + 1N 2 (g) 1Mg 3 N 2 (s) B. 3) 2, 3, 2 2Al(s) + 3Cl 2 (g) 2AlCl 3 (s) B. Al(s) + Cl 2 (g) AlCl 3 (s) 1) 3, 3, 2 2) 1, 3, 1 3) 2, 3, Equations with Polyatomic Ions Balancing with Polyatomic Ions Na 3 PO 4 (aq) + MgCl 2 (aq) Mg 3 (PO 4 ) 2 (s) + NaCl(aq) Balance PO 3-4 as a unit 2Na 3 PO 4 (aq) + MgCl 2 (aq) Mg 3 (PO 4 ) 2 (s) + NaCl(aq) 2 PO 3-4 = 2 PO 3-4 Check Na + balance 6 Na + = 6 Na + 2Na 3 PO 4 (aq) + 3MgCl 2 (aq) Mg 3 ( PO 4 (s) + 6NaCl(aq) Balance Mg and Cl 2Na 3 PO 4 (aq) + 3MgCl 2 (aq) Mg 3 (PO 4 ) 2 (s) + 6NaCl(aq) 3 Mg 2+ = 3 Mg 2+ 6 Cl - = 6 Cl

13 Balance and list the coefficients from reactants to products. A. Fe 2 O 3 (s) + C(s) Fe(s) + CO 2 (g) 1) 2, 3, 2, 3 2) 2, 3, 4, 3 3) 1, 1, 2, 3 B. Al(s) + FeO(s) Fe(s) + Al 2 O 3 (s) 1) 2, 3, 3, 1 2) 2, 1, 1, 1 3) 3, 3, 3, 1 A. 2) 2, 3, 4, 3 2Fe 2 O 3 (s)+ 3C(s) 4Fe(s) + 3CO 2 (g) B. 1) 2, 3, 3, 1 2Al(s) + 3FeO(s) 3Fe(s) + 1Al 2 O 3 (s) C. 2) 2, 3, 1, 3 2Al(s) + 3H 2 SO 4 (aq) 1Al 2 (SO 4 ) 3 (aq) + 3H 2 (g) C. Al(s) + H 2 SO 4 (aq) Al 2 (SO 4 ) 3 (aq) + H 2 (g) 1) 3, 2, 1, 2 2) 2, 3, 1, 3 3) 2, 3, 2, Chapter 5 Chemical Quantities and Reactions 5.5 Types of Reactions Type of Reactions Chemical reactions can be classified as combination reactions. decomposition reactions. single replacement reactions. double replacement reactions Combination Formation of MgO In a combination reaction, two or more elements form one product. or simple compounds combine to form one product. A + B A B 2Mg(s) + O 2 (g) 2Na(s) + Cl 2 (g) SO 3 (g) + H 2 O(l) 2MgO(s) 2NaCl(s) H 2 SO 4 (aq) 77 78

14 Decomposition Decomposition of HgO In a decomposition reaction, one substance splits into two or more simpler substances. 2HgO(s) 2KClO 3 (s) 2Hg(l) + O 2 (g) 2KCl(s) + 3 O 2 (g) Classify the following reactions as 1) combination or 2) decomposition. Classify the following reactions as 1) combination or 2) decomposition. A. H 2 (g) + Br 2 (g) B. Al 2 (CO 3 ) 3 (s) C. 4Al(s) + 3C(s) 2HBr(l) Al 2 O 3 (s) + 3CO 2 (g) Al 4 C 3 (s) 1 A. H 2 (g) + Br 2 (g) 2HBr(l) 2 B. Al 2 (CO 3 ) 3 (s) Al 2 O 3 (s) + 3CO 2 (g) 1 C. 4Al(s) + 3C(s) Al 4 C 3 (s) Single Replacement Zn and HCl is a Single Replacement Reaction In a single replacement reaction, one element takes the place of a different element in another reacting compound. Zn(s) + 2HCl(aq) ZnCl 2 (aq) + H 2 (g) Fe(s) + CuSO 4 (aq) FeSO 4 (aq) + Cu(s) 83 84

15 Double Replacement Example of a Double Replacement In a double replacement, two elements in the reactants exchange places. AgNO 3 (aq) + NaCl(aq) AgCl(s) + NaNO 3 (aq) ZnS(s) + 2HCl(aq) ZnCl 2 (aq) + H 2 S(g) Classify the following reactions as 1) single replacement or 2) double replacement. A. 2Al(s) + 3H 2 SO 4 (aq) Al 2 (SO 4 ) 3 (s) + 3H 2 (g) B. Na 2 SO 4 (aq) + 2AgNO 3 (aq) Ag 2 SO 4 (s) + 2NaNO 3 (aq) C. 3C(s) + Fe 2 O 3 (s) 2Fe(s) + 3CO(g) Classify the following reactions as 1) single replacement or 2) double replacement. 1 A. 2Al(s) + 3H 2 SO 4 (aq) Al 2 (SO 4 ) 3 (s) + 3H 2 (g) 2 B. Na 2 SO 4 (aq) + 2AgNO 3 (aq) Ag 2 SO 4 (s) + 2NaNO 3 (aq) 1 C. 3C(s) + Fe 2 O 3 (s) 2Fe(s) + 3CO(g) Identify each reaction as 1) combination, 2) decomposition, 3) single replacement, or 4) double replacement. A. 3Ba(s) + N 2 (g) Ba 3 N 2 (s) B. 2Ag(s) + H 2 S(aq) Ag 2 S(s) + H 2 (g) C. SiO 2 (s) + 4HF(aq) SiF 4 (s) + 2H 2 O(l) D. PbCl 2 (aq) + K 2 SO 4 (aq) 2KCl(aq) + PbSO 4 (s) E. K 2 CO 3 (s) K 2 O(aq) + CO 2 (g) 1 A. 3Ba(s) + N 2 (g) Ba 3 N 2 (s) 3 B. 2Ag(s) + H 2 S(aq) Ag 2 S(s) + H 2 (g) 4 C. SiO 2 (s) + 4HF(aq) SiF 4 (s) + 2H 2 O(l) 4 D. PbCl 2 (aq) + K 2 SO 4 (aq) 2KCl(aq) +PbSO 4 (s) 2 E. K 2 CO 3 (s) K 2 O(aq) + CO 2 (g) 89 90

16 Each of the following reactions occur in the formation of smog or acid rain. Identify the type of reaction and balance each. A. NO(g) + O 2 (g) NO 2 (s) B. N 2 (g) + O 2 (g) NO(g) C. SO 2 (g) + O 2 (g) SO 3 (g) D. NO 2 (g) NO(g) + O(g) Each of the following reactions occur in the formation of smog or acid rain. Identify the type of reaction and balance each. Combination A. 2NO(g) + O 2 (g) 2NO 2 (s) B. N 2 (g) + O 2 (g) 2NO(g) C. 2SO 2 (g) + O 2 (g) 2SO 3 (g) Decomposition D. NO 2 (g) NO(g) + O(g) Chapter 5 Chemical Quantities and Reactions 5.6 Oxidation-Reduction Reactions Oxidation and Reduction An oxidation-reduction reaction provides us with energy from food. provides electrical energy in batteries. occurs when iron rusts. 4Fe(s) + 3O 2 (g) 2Fe 2 O 3 (s) Electron Loss and Gain Oxidation and Reduction An oxidation-reduction reaction involves a transfer of electrons from one reactant to another. oxidation as a loss of electrons (LEO). reduction as a gain of electrons (GER)

17 Zn and Cu 2+ Electron Transfer from Zn to Cu 2+ Oxidation: loss of electrons Zn(s) Zn 2+ (aq) + 2e- oxidation silver metal Cu 2+ (aq) + 2e- Cu(s) reduction blue solution orange Reduction: gain of electrons Identify each of the following as 1) oxidation or 2) reduction. A. Sn(s) Sn 4+ (aq) + 4e B. Fe 3+ (aq) + 1e Fe 2+ (aq) C. Cl 2 (g) + 2e 2Cl - (aq) Identify each of the following as 1) oxidation or 2) reduction. 1 A. Sn(s) Sn 4+ (aq)+ 4e 2 B Fe 3+ (aq) + 1e Fe 2+ (aq) 2 C. Cl 2 (g) + 2e 2Cl - (aq) Writing Oxidation and Reduction Reactions Write the separate oxidation and reduction reactions for the following equation. 2Cs(s) + F 2 (g) 2CsF(s) A cesium atom loses an electron to form cesium ion. Cs(s) Cs + (s) + 1e oxidation Fluorine atoms gain electrons to form fluoride ions. F 2 (s) + 2e - 2F (s) reduction In light-sensitive sunglasses, UV light initiates an oxidation-reduction reaction. uv light Ag + + Cl Ag + Cl A. Which reactant is oxidized? B. Which reactant is reduced?

18 In light-sensitive sunglasses, UV light initiates an oxidation-reduction reaction. uv light Ag + + Cl Ag + Cl A. Which reactant is oxidized? Cl Cl + 1e Identify the substances that are oxidized and reduced in each of the following reactions. A. Mg(s) + 2H + (aq) Mg 2+ (aq) + H 2 (g) B. 2Al(s) + 3Br 2 (g) 2AlBr 3 (s) B. Which reactant is reduced? Ag + + 1e Ag A. Mg is oxidized. Mg(s) Mg 2+ (aq) + 2e H + is reduced. 2H + + 2e H 2 B. Al is oxidized. Al Al e Br is reduced. Br + e Br Chapter 5 Chemical Quantities and Reactions 5.7 Mole Relationships in Chemical Equations Law of Conservation of Mass Conservation of Mass The law of conservation of mass indicates that in an ordinary chemical reaction, matter cannot be created or destroyed. no change in total mass occurs in a reaction. mass of products is equal to mass of reactants. Copyright 2009 by Pearson Education, Inc 2 moles of Ag + 1 mole of S = 1 mole of Ag 2 S 2 (107.9 g) + 1(32.1 g) = 1 (247.9 g) g reactants = g product

19 Reading Equations in Moles Writing Mole-Mole Factors Consider the following equation: 4 Fe(s) + 3 O 2 (g) 2 Fe 2 O 3 (s) This equation can be read in moles by placing the word moles of between each coefficient and formula. 4 moles of Fe + 3 moles of O 2 2 moles of Fe 2 O 3 A mole-mole factor is a ratio of the moles for any two substances in an equation. 4Fe(s) + 3O 2 (g) 2Fe 2 O 3 (s) Fe and O 2 4 moles Fe and 3 moles O 2 3 moles O 2 4 moles Fe Fe and Fe 2 O 3 4 moles Fe and 2 moles Fe 2 O 3 2 moles Fe 2 O 3 4 moles Fe O 2 and Fe 2 O 3 3 moles O 2 and 2 moles Fe 2 O 3 2 moles Fe 2 O 3 3 moles O Consider the following equation: 3H 2 (g) + N 2 (g) 2NH 3 (g) A. A mole-mole factor for H 2 and N 2 is 1) 3 moles N 2 2) 1 mole N 2 3) 1 mole N 2 1 mole H 2 3 moles H 2 2 moles H 2 B. A mole-mole factor for NH 3 and H 2 is 1) 1 mole H 2 2) 2 moles NH 3 3) 3 moles N 2 2 moles NH 3 3 moles H 2 2 moles NH 3 3H 2 (g) + N 2 (g) 2NH 3 (g) A. A mole-mole factor for H 2 and N 2 is 2) 1 mole N 2 3 moles H 2 B. A mole-mole factor for NH 3 and H 2 is 2) 2 moles NH 3 3 moles H Calculations with Mole Factors Guide to Using Mole Factors How many moles of Fe 2 O 3 can form from 6.0 moles of O 2? 4Fe(s) + 3O 2 (g) 2Fe 2 O 3 (s) Relationship: 3 mole O 2 = 2 mole Fe 2 O 3 Use a mole-mole factor to determine the moles of Fe 2 O mole O 2 x 2 mole Fe 2 O 3 = 4.0 moles of Fe 2 O 3 3 mole O

20 How many moles of Fe are needed for the reaction of 12.0 moles of O 2? 4Fe(s) + 3O 2 (g) 2Fe 2 O 3 (s) 1) 3.00 moles of Fe 2) 9.00 moles of Fe 3) 16.0 moles of Fe Study Tip: Mole Factors In a problem, identify the compounds given and needed. How many moles of Fe are needed for the reaction of 12.0 moles of O 2? 4Fe(s) + 3O 2 (g) 2Fe 2 O 3 (s) The possible mole factors for the solution are 4 moles Fe and 3 moles O 2 3 moles O 2 4 moles Fe ) 16.0 moles of Fe 12.0 moles O 2 x 4 moles Fe = 16.0 moles of Fe 3 moles O 2 Chapter 5 Chemical Quantities and Reactions 5.8 Mass Calculations for Reactions Moles to Grams Moles to Grams Suppose we want to determine the mass (g) of NH 3 that can form from 2.50 moles of N 2. N 2 (g) + 3H 2 (g) The plan needed would be 2NH 3 (g) moles N 2 moles NH 3 grams NH 3 The setup for the solution would be: 2.50 mole N 2 x 2 moles NH 3 x 17.0 g NH 3 1 mole N 2 1 mole NH 3 given mole-mole factor molar mass = 85.0 g of NH 3 The factors needed would be: mole factor NH 3 /N 2 and the molar mass NH

21 How many grams of O 2 are needed to produce mole of Fe 2 O 3 in the following reaction? 2) 19.2 g of O 2 4Fe(s) + 3O 2 (g) 2Fe 2 O 3 (s) 1) 38.4 g of O 2 2) 19.2 g of O 2 3) 1.90 g of O mole Fe 2 O 3 x 3 mole O 2 x 32.0 g O 2 = 19.2 g of O 2 2 mole Fe 2 O 3 1 mole O 2 mole factor molar mass Calculating the Mass of a Reactant Calculating the Mass of a Reactant The reaction between H 2 and O 2 produces 13.1 g of water. How many grams of O 2 reacted? 2 H 2 (g) + O 2 (g) 2 H 2 O(g)? g 13.1 g The plan and factors would be g H 2 O mole H 2 O mole O 2 g of O 2 molar mole-mole molar mass H 2 O factor mass O 2 The setup would be: 13.1 g H 2 O x 1 mole H 2 O x 1 mole O 2 x 32.0 g O g H 2 O 2 moles H 2 O 1 mole O 2 molar mole-mole molar mass H 2 O factor mass O 2 = 11.6 g of O Acetylene gas, C 2 H 2, burns in the oxyacetylene torch for welding. How many grams of C 2 H 2 are burned if the reaction produces 75.0 g of CO 2? 2C 2 H 2 (g) + 5O 2 (g) 4CO 2 (g) + 2H 2 O(g) 1) 88.6 g of C 2 H 2 2) 44.3 g of C 2 H 2 3) 22.2 g of C 2 H 2 3) 22.2 g of C 2 H 2 2C 2 H 2 (g) + 5O 2 (g) 4CO 2 (g) + 2H 2 O(g) 75.0 g CO 2 x 1 mole CO 2 x 2 moles C 2 H 2 x 26.0 g C 2 H g CO 2 4 moles CO 2 1 mole C 2 H 2 molar mole-mole molar mass CO 2 factor mass C 2 H 2 = 22.2 g of C 2 H

22 Calculating the Mass of Product When 18.6 g of ethane gas, C 2 H 6, burns in oxygen, how many grams of CO 2 are produced? 2C 2 H 6 (g) + 7O 2 (g) 4CO 2 (g) + 6H 2 O(g) 18.6 g? g The plan and factors would be g C 2 H 6 mole C 2 H 6 mole CO 2 g of CO 2 molar mole-mole molar mass C 2 H 6 factor mass CO 2 Calculating the Mass of Product 2C 2 H 6 (g) + 7O 2 (g) 4CO 2 (g) + 6H 2 O(g) The setup would be: 18.6 g C 2 H 6 x 1 mole C 2 H 6 x 4 moles CO 2 x 44.0 g CO g C 2 H 6 2 moles C 2 H 6 1 mole CO 2 molar mole-mole molar mass C 2 H 6 factor mass CO 2 = 54.4 g of CO Study Tip: Check Units Be sure to check that all units cancel to give the needed unit. Note each cancelled unit in the following setup: How many grams of H 2 O are produced when 35.8 g of C 3 H 8 react by the following equation? needed unit g C 2 H 6 x mole C 2 H 6 x moles CO 2 x g CO 2 g C 2 H 6 moles C 2 H 6 mole CO 2 molar mole-mole molar mass C 2 H 6 factor mass CO 2 C 3 H 8 (g) + 5O 2 (g) 1) 14.6 g of H 2 O 2) 58.6 g of H 2 O 3) 117 g of H 2 O 3CO 2 (g) + 4H 2 O(g) ) 58.6 g of H 2 O C 3 H 8 (g) + 5O 2 (g) 3CO 2 (g) + 4H 2 O(g) 35.8 g C 3 H 8 x 1 mole C 3 H 8 x 4 mole H 2 O x 18.0 g H 2 O 44.0 g C 3 H 8 1 mole C 3 H 8 1 mole H 2 O molar mole-mole molar mass C 3 H 8 factor mass H 2 O Chapter 5 Chemical Quantities and Reactions 5.9 Energy in Chemical Reactions = 58.6 g of H 2 O

23 Collision Theory of Reactions Activation Energy A chemical reaction occurs when collisions between molecules have sufficient energy to break the bonds in the reactants. bonds between atoms of the reactants (N 2 and O 2 ) are broken and new bonds (NO) can form. The activation energy is the minimum energy needed for a reaction to take place. When a collision provides energy equal to or greater than the activation energy, product can form Exothermic Reactions Endothermic Reactions In an exothermic reaction, heat is released. the energy of the products is less than the energy of the reactants. heat is a product. C(s) + 2H 2 (g) CH 4 (g) + 18 kcal In an endothermic reaction Heat is absorbed. The energy of the products is greater than the energy of the reactants. Heat is a reactant (added). N2 (g) + O 2 (g) kcal 2NO(g) Identify each reaction as 1) exothermic or 2) endothermic. A. N 2 + 3H 2 2NH kcal B. CaCO kcal CaO + CO 2 C. 2SO 2 + O 2 2SO 3 + heat Identify each reaction as 1) exothermic or 2) endothermic. 1 A. N 2 + 3H 2 2NH kcal 2 B. CaCO kcal CaO + CO 2 1 C. 2SO 2 + O 2 2SO 3 + heat

24 Rate of Reaction Reaction Rate and Catalysts Reaction rate is the speed at which reactant is used up. is the speed at which product forms. increases when temperature rises because reacting molecules move faster, providing more colliding molecules with energy of activation. A catalyst increases the rate of a reaction. lowers the energy of activation. is not used up during the reaction Summary State the effect of each on the rate of reaction as: 1) increases 2) decreases 3) no change A. increasing the temperature. B. removing some of the reactants. C. adding a catalyst. D. placing the reaction flask in ice. E. increasing the concentration of one of the reactants State the effect of each on the rate of reaction as: 1) increases 2) decreases 3) no change 1 A. increasing the temperature. 2 B. removing some of the reactants. 1 C. adding a catalyst. 2 D. placing the reaction flask in ice. 1 E. increasing the concentration of one of the reactants. Indicate the effect of each factor listed on the rate of the following reaction as: 1) increases 2) decreases 3) none 2CO(g) + O 2 (g) 2CO 2 (g) A. raising the temperature B. adding O 2 C. adding a catalyst D. lowering the temperature

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