chemistry of matches p4s3 + kclo3 p2o5 + kcl + so2 d tetraphosphorus
DESCRIPTION
Chemical Equations and Reactions Chapter 8TRANSCRIPT
CHEMISTRY OF MATCHES
P4S3 + KClO3 P2O5 + KCl + SO2
tetraphosphorustrisulfide
potassiumchlorate
diphosphoruspentoxide
potassiumchloride
sulfurdioxide
D
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.
Charles H.Corwin, Introductory Chemistry 2005, page 182
Safety matches
The products from this reaction are P2O5, KCl, and SO2,the last of which is responsible for the characteristic sulfur smell.
Strike anywhere matchesThe substances P4S3 and KClO3 are separated. The P4S3 is onthe matchbox cover. Only when the chemicals combine do they react and produce a flame.
CHAPTER 8
Chemical Equations and Reactions
Describing Chemical Reactions
SECTION 1
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 THOUGHTSChemicalreactions
Chemicalequations
Chemicalequations
• Balancing equations
• Predicting products from reactants
• Synthesis• Decomposition• Single replacement• Double replacement• Combustion
Packard, Jacobs, Marshall, Chemistry Pearson AGS Globe, page 175
SIGNS OF CHEMICAL REACTIONSThere are five main signs that indicate a chemical reaction has taken place:
change in color change in odor production of newgases or vapor
input or releaseof energy
difficult to reverse
releaseinput
CHEMICAL EQUATIONSDepict the kind of reactants and products and their relative amounts in a reaction.
4 Al(s) + 3 O2(g) 2 Al2O3(s)
The numbers in the front are called stoichiometric coefficients.
The letters (s), (g), and (l) are the physical states of compounds.
reactants product
aluminum oxide
CHEMICAL EQUATIONS
This equation means:
4 Al(s) + 3 O2(g) 2 Al2O3(s)
4 Al atoms + 3 O2 molecules yield 2 molecules of Al2O3
4 Al moles + 3 O2 moles yield 2 moles of Al2O3
or
4 g Al + 3 g O2 yield 2 g Al2O3
4 mol Al@27g/mol 3 mol O2@32g/mol 2 mol Al2O3@102g/mol108 g + 96 g = 204 g
aluminum oxide sandpaper
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 EQUATION1. 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).
1. H2O(l) H2(g) + O2(g)
2. 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.
H2O(l) H2(g) + O2(g)
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
sideProduct
sideH 4 4O 2 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 COEFFICIENTSZn(s) + HCl(aq) ZnCl2(aq) + H2(g)
Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)
Count atoms:Zn – 1 on left, 1 on rightH – 2 on left, 2 on rightCl – 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 ReactionsSECTION 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)
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
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 →No reaction 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