Chemistry of Matches P4S3 + KClO3 P2O5 + KCl + SO2 D tetraphosphorus trisulfide potassium chlorate diphosphorus pentoxide potassium chloride sulfur dioxide                                                     Strike anywhere matches Safety matches The substances P4S3 and KClO3 are present on the tip of a match. When the match is struck on a rough surface, the two chemicals (reactants) ignite and produce a flame. The products from this reaction are P2O5, KCl, and SO2, the last which is responsible for the characteristic sulfur smell. Safety matches have the P4S3 on the matchbook or box. This is the red strip you need to rub the match against to get it to ignite. Strike anywhere matches contain both reactants on the match head. [NOTE: Red phosphorus is an important ingredient for making methamphetamines – and may be reason high school teachers are not allowed to purchase it.] A good demonstration is the SMOKE reaction: combine 6 g KClO3 + 2 g table sugar (stir gently) and place in an evaporating dish. Add 1 drop of [H2SO4]. The sugar will rapidly burn! Do this reaction only in a fume hood. It will produce lots of smoke. The rapid combustion of the sugar is due to the fact that the potassium chlorate is an oxidizer (contains oxygen). Oxygen is not the limiting reactant for this demonstration. I also show the DEHYDRATION OF SUGAR demonstration. I ½ fill a 250 mL beaker with table sugar, add ~5 mL tap water and stir with a glass stirring rod. Finally, add ~50 mL concentrated sulfuric acid. The sugar will be rapidly dehydrated (leaving only a carbon tower). DO NOT touch the burned sugar as it contains excess sulfuric acid. This reaction is a much slower burning of table sugar…not enough oxygen present. The substances P4S3 and KClO3 are both present on the tip of a strike anywhere match. When the match is struck on a rough surface, the two chemicals (reactants) ignite and produce a flame. The substances P4S3 and KClO3 are separated. The P4S3 is on the matchbox cover. Only when the chemicals combine do they react and produce a flame. The products from this reaction are P2O5, KCl, and SO2,the last of which is responsible for the characteristic sulfur smell. Charles H.Corwin, Introductory Chemistry 2005, page 182

Chemical Equations and Reactions Chapter 8

Describing Chemical Reactions Section 1

(NH4)2Cr2O7 (s)  N2(g) + Cr2O3(s) + 4H2O(g) Chemical reaction  process by which one or more substances are changed into one or more different substances Represented by chemical equations  represents, with symbols and formulas, the identities and relative amounts of the reactants and products in a chemical reaction (NH4)2Cr2O7 (s)  N2(g) + Cr2O3(s) + 4H2O(g)

Organize Your Thoughts Chemical reactions Chemical equations Chemical equations To identify the reactants and products in a chemical equation. To balance a chemical equation with coefficients. To identify synthesis (combination), decomposition, and combustion reactions. To identify single-replacement reactions. To identify double-replacement reactions. To predict the products of a reaction. Synthesis Decomposition Single replacement Double replacement Combustion Balancing equations Predicting products from reactants Packard, Jacobs, Marshall, Chemistry Pearson AGS Globe, page 175

Signs of Chemical Reactions There are five main signs that indicate a chemical reaction has taken place: release input change in color change in odor production of new gases or vapor input or release of energy difficult to reverse

Chemical Equations Depict the kind of reactants and products aluminum oxide Depict the kind of reactants and products and their relative amounts in a reaction. reactants product 4 Al(s) + 3 O2(g) 2 Al2O3(s) A chemical equation is an expression that gives the identities and quantities of the substances in a chemical reaction Chemical formulas and other symbols are used to indicate the starting material(s) or reactant(s), which are written on the left side of the equation, and the final compound(s) or product(s), which are written on the right side. An arrow, read as yields or reacts to form, points from the reactants to the products. Abbreviations are added in parentheses as subscripts to indicate the physical state of each species:—(s) for solid, (l) for liquid, (g) for gas, and (aq) for an aqueous solution. A balanced chemical equation is when both the numbers of each type of atom and the total charge are the same on both sides. A chemical reaction represents a change in the distribution of atoms but not in the number of atoms. http://img.alibaba.com/photo/10784694/Aluminum_Oxide_Abrasive_Fine_Grit_120_220_.jpg http://upload.wikimedia.org/wikipedia/commons/thumb/f/f2/Corundum_Aluminum_Oxide_Gallantin_Co_MontanaDSC03201.jpg/600px-Corundum_Aluminum_Oxide_Gallantin_Co_MontanaDSC03201.jpg http://www.germes-online.com/direct/dbimage/50327532/Aluminum_Alloy_Pipe.jpg The letters (s), (g), and (l) are the physical states of compounds. The numbers in the front are called stoichiometric coefficients.

Chemical Equations 4 Al(s) + 3 O2(g) 2 Al2O3(s) aluminum oxide sandpaper 4 Al(s) + 3 O2(g) 2 Al2O3(s) 4 g Al + 3 g O2 yield 2 g Al2O3 This equation means: 4 Al atoms + 3 O2 molecules yield 2 molecules of Al2O3 or 4 Al moles + 3 O2 moles yield 2 moles of Al2O3 4 mol Al@27g/mol 3 mol O2@32g/mol 2 mol Al2O3@102g/mol 108 g + 96 g = 204 g

CH4(g) + O2(g)  CO2(g) + H2O(g) Formula equations Formula equation  represents reactants and products of chemical reaction by their symbols or formulas CH4(g) + O2(g)  CO2(g) + H2O(g) Is the law of conservation of mass satisfied here?

CH4 + O2  CO2 + H2O Reactants – 7 atoms Products – 6 atoms Hydrogen = 4 on left, = 2 on right Oxygen = 2 on left, = 3 on right In order to satisfy law of conservation of mass, must balance the equation by adding coefficients

Balancing a Chemical Equation Write a formula equation by substituting correct formulas for the names of the reactants and products (if you do not start with a formula equation). H2O(l)  H2(g) + O2(g) Balance the formula equation according to the law of conservation of mass. There are a few simple guidelines to use for this…..

Guidelines for Balancing Equations Balance the different types of atoms one at a time. First balance the atoms of elements that are combined and that appear only once on each side of the equation. Balance polyatomic ions that appear on both sides as single units. Balance H and O atoms (or any other lone atoms) last.

2H2O(l)  2H2(g) + O2(g) ---- balanced! 2 oxygen on right and only 1 on the left Start with placing 2 in front of H2O 2H2O(l)  H2(g) + O2(g) Oxygen is now balance with 2 on left and 2 on right Now balance hydrogen – 4 on left, 2 on right Add coefficient 2 to H2 2H2O(l)  2H2(g) + O2(g) ---- balanced!

DO NOT!..... DO NOT WRITE INCORRECT FORMULAS, THIS WILL MESS UP YOUR BALANCING DO NOT CHANGE SUBSCRIPTS IN FORMULAS TO BALANCE THE EQUATION! H2O(l)  H2(g) + O2(g) H2O(l)  H2(g) + O(g)

DO!!!!..... When you think you have balanced the equation, COUNT THE NUMBERS OF EACH TYPE OF ATOM ON EITHER SIDE OF THE EQUATION 2H2O(l)  2H2(g) + O2(g) Reactant side Product side H 4 O 2

Sample Problem The reaction of zinc with aqueous hydrochloric acid produces a solution of zinc chloride and hydrogen gas. Write a balanced equation for the reaction.

1. Write the word equation Zinc + hydrochloric acid  zinc chloride + hydrogen 2. Write the formula equation Zn(s) + HCl(aq)  ZnCl2(aq) + H2(g)

Adjust the coefficients Zn(s) + HCl(aq)  ZnCl2(aq) + H2(g) Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2(g) Count atoms: Zn – 1 on left, 1 on right H – 2 on left, 2 on right Cl – 2 on left, 2 on right

Practice Problem 1a Write word, formula, and balanced chemical equations for magnesium and hydrochloric acid react to produce magnesium chloride and hydrogen. Magnesium + hydrochloric acid  magnesium chloride + hydrogen Mg + HCl  MgCl2 + H2 Mg + 2HCl  MgCl2 + H2

Practice Problem 1b Write word, formula, and balanced chemical equations for silicon dioxide and hydrofluoric acid reacting to produce silicon tetrafluoride and water. Silicon dioxide+ hydrofluoric acid  silicon tetrafluoride + water SiO2+ HF  SiF4 + H2O SiO2+ 4HF  SiF4 + 2H2O

Practice Problem 2 Write word, formula and balanced equations for aqueous nitric acid reacts with solid magnesium hydroxide to produce aqueous magnesium nitrate and water. Nitric acid + magnesium hydroxide  magnesium nitrate + water HNO3(aq) + Mg(OH)2(s)  Mg(NO3)2(aq) + H2O(l) 2HNO3(aq) + Mg(OH)2(s)  Mg(NO3)2(aq) + 2H2O(l)

Practice Problem 3 Ammonium sulfate crystals are made by treating ammonia gas, often a by-product from coke-ovens, with aqueous sulfuric acid: 2 NH3(g) + H2SO4(aq) → (NH4)2SO4(s)

Practice Problem 4 Aluminum sulfate and calcium hydroxide are used in a water-purification process. When added to water, they dissolve and react to produce 2 insoluble products, aluminum hydroxide and calcium sulfate. Write a balanced equation for this reaction. Al2(SO4)3(aq) + 3Ca(OH)2(aq)  2Al(OH)3(s) + 3CaSO4(s)

Practice Problem 5 Write balanced chemical equations for the following reaction: Solid sodium combines with chlorine gas to produce solid sodium chloride. 2Na(s) + Cl2(g) → 2NaCl(s)

Practice Problem 6 When solid copper reacts with aqueous silver nitrate, the products are aqueous copper(II) nitrate and solid silver. Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq) + 2Ag(s)

Practice Problem 7 In a blast furnace, the reaction between solid iron(III) oxide and carbon monoxide gas produces solid iron and carbon dioxide gas. Fe2O3(s) + 3CO(g) → 2Fe(s) + 3CO2(g)

Types of Chemical Reactions Section 2

1. Decomposition Reactions Decomposition reaction  a single compound has a reaction that makes two or more simpler substances General equation AX  A + X Most happen when energy (light/heat) is added

2. Synthesis Reactions Synthesis (composition) reaction  two or more substances combine to form a new compound General equation A + X  AX

3. Single-Replacement Reactions Single-replacement reaction  one element replaces a similar element in a compound General equation A + BX  AX + B Y + BX  BY + X

4. DOUBLE REPLACEMENT REACTIONS Double-replacement reaction  ions of two compounds exchange places in an aqueous solution to form two new compounds General equation AX + BY  AY + BX

5. Combustion Reactions Combustion reaction  substance combines with oxygen, releasing large amount of energy as heat and light 2H2(g) + O2(g) → 2H2O(g)

Reactions of Elements with Oxygen and Sulfur One simple type of synthesis reaction is combination of element with oxygen to form an oxide of the element Almost all metals react with oxygen to form oxides Ex. Magnesium burned  magnesium oxide

2Mg(s) + O2(g)  2MgO(s)

Group 2 Elements Group 2 elements react to form oxides with general formula MO M represents metal Group 1 metals form oxides with general formula M2O Li + O2  Li2O

Reactions with Sulfur Groups 1 and 2 react with sulfur to make sulfides of the element Group 1  M2S Group 2  MS 16Rb(s) + S8(s) → 8Rb2S(s) 8Ba(s) + S8(s) → 8BaS(s)

Some metals (usually transition metals) combine with O2 to make two different oxides Ex. Fe – can be +2 or +3 2Fe(s) + O2(g) → 2FeO(s) 4Fe(s) + 3O2(g) → 2Fe2O3(s)

Nonmetals Nonmetals also react with oxygen to make oxides Sulfur reacts with oxygen to make sulfur dioxide When carbon is burned, it makes carbon dioxide S8(s) + 8O2(g) → 8SO2(g) C(s) + O2(g) → CO2(g)

Hydrogen reacts with oxygen to make dihydrogen monoxide 2H2(g) + O2(g) → 2H2O(g)

Reactions of Metals & Halogens Most metals react with halogens to make either ionic or covalent compounds Ex. Group 1 reacts with halogens to form ionic compounds with formula MX M = metal, X = halogen 2Na(s) + Cl2(g) → 2NaCl(s) 2K(s) + I2(g) → 2KI(s) Reactions of Metals & Halogens

Group 2 Metals & Halogens Formula MX2 Mg(s) + F2(g) → MgF2(s) Sr(s) + Br2(l) → SrBr2(s)

Synthesis Reactions with Oxides Active metals  highly reactive metals Oxides of active metals react with water to make metal hydroxides CaO(s) + H2O(l) → Ca(OH)2(s) CaO = lime Ca(OH)2 is important in setting cement Synthesis Reactions with Oxides

Oxyacids Many oxides of nonmetals react with water to make oxyacids SO2(g) + H2O(l) → H2SO3(aq) In air polluted with SO2, reacts with oxygen in air to form sulfuric acid (acid rain) 2H2SO3(aq) + O2(g) → 2H2SO4(aq)

Practice Problems Identify the products in each of the following reactions: a. hydrogen burned in oxygen H2O b. H2(g) + N2(g)  NH3 c. CaO(s) + H2O(l)  Ca(OH)2(aq)

Decomposition of Binary Compounds Simplest kind of decomposition reaction is binary compound into its elements Ex. Passing electricity through water 2H2O(l) 2H2(g) + O2(g) electricity

Electrolysis  decomposition of a substance by electricity

Oxides of less-active metals (lower center of PT) decompose into elements when heated Δ 2HgO(s)  2Hg(l) + O2(g)

Decomposition of Metal Carbonates When heated, metal carbonates break down to make a metal oxide and CO2 Δ CaCO3(s)  CaO(s) + CO2(g)

Decomposition of Metal Hydroxides All except with Group 1 metals decompose when heated to make metal oxides and water Δ Ca(OH)2(s)  CaO(s) + H2O(g)

Decomposition of Metal Chlorates When heated, metal chlorates decompose to make metal chloride and oxygen Δ 2KClO3(s) 2KCl(s) + 3O2(g) MnO2(s)

Decomposition of Acids Certain acids decompose into nonmetal oxides and water H2CO3(aq) → CO2(g) + H2O(l) Δ H2SO4(aq)  SO3(g) + H2O(l)

Practice Problems Predict the products for these decomposition reactions a. sodium chlorate  Sodium chloride + oxygen b. calcium carbonate  Calcium oxide + carbon dioxide c. potassium bromide  Potassium + bromine

Replacement of a Metal in a Compound by Another Metal Aluminum is more active than lead When solid aluminum is placed in aqueous lead(II) nitrate, the aluminum replaces the lead 2Al(s) + 3Pb(NO3)2(aq) → 3Pb(s) + 2Al(NO3)3(aq) Based on activity series of metals

Replacement of Hydrogen in Water by Metal Most-active metals (Group 1) react strongly with water to make metal hydroxides and hydrogen 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g) Less-active metals react with steam or other form of energy

Replacement of Hydrogen in Acid by Metal More-active metals react with certain acidic solutions and replace hydrogen Reaction products are metal compound (salt) and hydrogen gas Mg(s) + 2HCl(aq) → H2(g) + MgCl2(aq)

Replacement of Halogens One halogen replaces another Fluorine is most reactive Can replace any other halogen Cl2(g) + 2KBr(aq) → 2KCl(aq) + Br2(l) F2(g) + 2NaCl(aq) → 2NaF(aq) + Cl2(g) Br2(l) + KCl(aq) → no reaction

Practice Problems For the following equations, predict what the products will be: a. Ag + KNO3 → No reaction b. Zn + AgNO3 → Zn(NO3)2 + Ag c. Cl2 + KI → I2 + 2KCl

d. Cu + FeSO4 → No reaction e. Fe + Pb(NO3)2 → Pb + Fe(NO3)2 f. Cu + Al2(SO4)3 → g. Al + Pb(NO3)2 → Pb + Al(NO3)3 h. Cl2 + NaI → I2 + NaCl

i. Fe + AgC2H3O2 → Fe(C2H3O2)2 + Ag j. Al + CuCl2 → Cu + Al2Cl3 k. Br2 + CaI2 → I2 + CaBr2 l. Fe + CuSO4 → FeSO4 + Cu m. Cl2 + MgI2 → I2 + MgCl2

Formation of a Precipitate Occurs when cations of one reactant combine with anions of another to form insoluble (or slightly soluble) compound 2KI(aq) + Pb(NO3)2(aq) → PbI2(s) + 2KNO3(aq)

Formation of a Gas In some D-R reactions, one product is insoluble gas that bubbles out of mixture FeS(s) + 2HCl(aq) → H2S(g) + FeCl2(aq)

Formation of Water In some D-R reactions, water is one of the products HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

Practice Problems Classify each of the following reactions as synthesis, decomposition, single-replacement, double-replacement, or combustion: a. N2(g) + 3H2(g) → 2NH3(g) synthesis b. 2Li(s) + 2H2O(l ) → 2LiOH(aq) + H2(g) single-replacement c. 2NaNO3(s) → 2NaNO2(s) + O2(g) decomposition

d. 2C6H14(l ) + 19O2(g) →12CO2(g) + 14H2O(l ) combustion e. NH4Cl(s) → NH3(g) + HCl(g) decomposition f. BaO(s) + H2O(l ) → Ba(OH)2(aq) synthesis g. AgNO3(aq) + NaCl(aq) →AgCl(s) + NaNO3(aq) double-replacement

Practice Problem For each of the following reactions, identify the missing substances, then balance the final equation. Each slot may be one OR MORE substances. a. synthesis: _____ → Li2O 4Li + O2  2Li2O b. decomposition: Mg(ClO3)2 → _____ Mg(ClO3)2  MgCl2 + 3O2

c. single-replacement: Na + H2O → _____ 2Na + 2H2O  2NaOH + H2 d. double-replacement: HNO3 + Ca(OH)2 → _____ 2HNO3 + Ca(OH)2  Ca(NO3)2 + 2H2O e. combustion: C5H12 + O2 → _____ C5H12 + 8O2  5CO2 + 6H2O