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Chapter Medley: Chemical Equations and Reactions To help you with upcoming Chem 101 lab experiments, we will combine the various types of chemical reactions into this mid-quarter chapter medley.

I. Writing and Balancing Chemical Equations (Ch 6.6) II. Types of Chemical Reactions

A. Combination Reactions (Ch 9.1) B. Decomposition Reactions (Ch 9.1) C. Single-Replacement Reactions (Ch 9.1) D. Double-Replacement Reactions (Ch 9.1)

Solubility Rules (Ch 8.4) E. Combustion Reactions (Ch 9.1) F. Oxidation – Reduction Reactions (Ch. 9.2 & 9.3) Supplemental Material: Comparing Strength of Agents G. Acid-Base Neutralization Reactions (Ch 10.1, 10.6 &

10.7)

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I. Writing and Balancing Chemical Equations (Ch 6.6) demo: Combustion of ethanol Reactant → Products ethanol + oxygen → carbon dioxide + water

C2H6O + 3 O2 → 2 CO2 + 3 H2O Balanced Equation Law of Conservation of Mass An equation coefficient is a multiplier that applies to all atoms and subscripts. It changes the amount, but not the _____________, of the substance. A coefficient of 1 in a balanced equation is not explicitly written.

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Physical states of reactants and products may be indicated: (s) for solid (l) for liquid (g) for gas 4 Fe(s) + 3 O2(g) → 2 Fe2O3(s) Reactions of substances in _______ solution are indicated by the symbol (aq), meaning aqueous: Zn(s) + 2 HCl(aq) → ZnCl2(aq) + H2(g)

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A capital Greek delta (∆) placed above the arrow indicates that the reaction occurs at ______________. The actual temperature required also may be written above or below the arrow. ∆ 350oC The symbol for a catalyst may also appear above or below the arrow. A catalyst increases the _______ of the reaction but is not consumed. Pt CH =CH (g) + H (g) CH3− CH3(g) 2 2 2 200oC

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Guidelines for Balancing Chemical Equations • Begin with an element that appears in only a single

substance on each side of the equation. • If there are several such elements, select the substance

that has the largest number of atoms of a single element.

• To balance an equation, change only coefficients in

front. NEVER change _______________. • Proceed to balance the atoms of other elements by the

same process. Check to see if balancing one element in a substance has caused others to become unbalanced and make necessary corrections.

• Balance atoms that appear in two or more places on

one side of the equation. • Check and reduce all coefficients to smallest set of

whole numbers (eliminate fractions).

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Practice Problem of Balancing an Equation FeI2 + Cl2 → FeCl3 + I2 (unbalanced) 1. balance Cl atoms

FeI2 + 3 Cl2 → 2 FeCl3 + I2 (unbalanced) 2. balance Fe atoms

2 FeI2 + 3 Cl2 → 2 FeCl3 + I2 (unbalanced) 3. balance I atoms

2 FeI2 + 3 Cl2 → 2 FeCl3 + 2 I2 balanced Do a final check by counting atoms on each side! 2 Fe 2 Fe 4 I 4 I 6 Cl 6 Cl

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Practice Problem

C3H8O + O2 → CO2 + H2O (unbalanced)

1. balance H (appears once on each side & in largest number)

C3H8O + O2 → CO2 + 4 H2O (unbalanced) 2. balance C

C3H8O + O2 → 3 CO2 + 4 H2O (unbalanced) 3. balance O

6 O atoms in CO2 + 4 O atoms in H2O 10 O atoms on product side - 1 O atom in C3H8O on reactant side 9 O atoms needed from O2 = 4 ½ molecules of O2 C3H8O + 4 ½ O2 → 3 CO2 + 4 H2O 4. eliminate fractions by multiplying the entire equation by 2; then check the final answer 2 C3H8O + 9 O2 → 6 CO2 + 8 H2O balanced 6 C, 16 H, 2+18 = 20 O → 6 C, 16 H, 12+8 = 20 O

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Drill Problem The white clouds are products of the reaction used to lift the space shuttle.

The solid propellants, aluminum powder and ammonium perchlorate, are more convenient to handle as rocket fuel. The white cloud is aluminum oxide. Balance the following reaction involved in the shuttle launch:

__Al(s) + __ NH4ClO4(s) → __ Al2O3(s) + __ AlCl3(s) + __NO(g) + __ H2O(g)

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Chemical Reactions may have one or more _____________: • Formation of a gas • Formation of a precipitate (an insoluble solid is formed) • Generation of a color or color change • Evolution or absorption of ________ (exothermic or endothermic reaction)

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A. Combination Reactions (Ch 9.1) A single product is produced from two or more reactants: X + Y → XY

2 H2 + O2 → 2 H2O (demo in lecture 1)

Figure 9.1 When a hot nail is stuck into a pile of zinc and sulfur, a fiery combination reaction occurs: Zn + S → ____

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Combination reactions with compounds as reactants:

2 NO2 + H2O2 → 2 HNO3 __________ nitrogen dioxide + hydrogen peroxide

Formation of ___________

SO3 + H2O → H2SO4 acidic oxide + water → acid

Jābir ibn Hayyān (721 – 815 AD) was a prominent polymath: a chemist and alchemist, astronomer and astrologer, engineer, geologist, philosopher, physicist, and pharmacist and physician. He is considered by some to be the "Father of Chemistry” and is better known under the name of Geber. Geber is credited with the discovery of sulfuric acid.

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B. Decomposition Reactions (Ch 9.1) A single reactant is converted into two or more products. XY → X + Y 2 NH3 → 3 H2 + N2 2 elements PF5 → PF3 + F2 compound & element ∆ CaCO3 → CaO + CO2 2 __________

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C. Single-Replacement Reactions (Ch 9.1) An atom or molecule replaces an atom or group of atoms from a compound. Most common = an element replaces another. Some metals replace other metals or hydrogen:

Fe + CuSO4 → Cu + FeSO4

Zn + 2 HCl → H2 + ________ Hydrogen can replace some metals:

CuO + H2 → Cu + H2O A nonmetal may replace another nonmetal:

Cl2 + NiI2 → I2 + NiCl2 F2 + 2 NaCl → Cl2 + 2 _______ Order of reactivity: F > Cl > Br > I F2 will replace all, I2 will replace _______

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D. Double-Replacement Reactions (Ch 9.1) Two substances exchange parts: AX + BY → AY + BX Complete chemical equation (demo)

Co(NO3)2(aq) + Na2CO3(aq) → CoCO3(s) + 2 NaNO3(aq) Ionic equation Soluble ionic compounds (salts) completely ____________ into ions in water:

Co2+ + 2NO3- + 2Na+ + CO3

2- → CoCO3(s) + 2Na+ + 2NO3-

Net ionic equation

Co2+ + CO32- → CoCO3(s)

Na+ and NO3

- are spectator ions. Formation of a _____________ drives the reaction. Learn to use the solubility rules to predict the products and to write the ionic and net ionic equation for any double-replacement reaction.

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Solubility Rules to Predict Possible Products (Ch 8.4)

Soluble - compound exists as ions in solution

Insoluble - compound will form a precipitate

No need to memorize these rules, a modified version of this table will be provided on exams or quizzes.

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Practice Problem: Use the solubility rules to predict the product for the following reaction. Then write a balanced chemical equation, the ionic equation, and the net ionic equation for this reaction. Identify the spectator ions.

KI (aq) + Pb(NO3)2(aq) → yellow ppt demo 2 colorless solutions We can write the complete chemical equation based on the fact that this is a double-replacement reaction in which two groups are exchanged:

2 KI (aq) + Pb(NO3)2(aq) → 2 KNO3(?) + PbI2(?) Now we check the solubility rules to identify which product is insoluble:

2 KI (aq) + Pb(NO ) (aq) → 2 KNO3(aq) + PbI2(s) 3 2 soluble insoluble

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2 KI (aq) + Pb(NO3)2(aq) → 2 KNO3(aq) + PbI2(s) Compounds that are soluble (aq) exist as ions in solution: 2K+ + 2I- + Pb2+ + 2NO3

- → 2K+ + 2NO3- + PbI2(s)

Ions that exist on both sides of the equation are spectator ions and can be omitted in the net ionic equation: Net Ionic Equation: __________________ Spectator Ions: _____________

Note that the spectator ions remain present in solution but they DO NOT participate in the reaction.

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Drill problems. Predict the outcomes: KI(aq) + Mg(NO3)2(aq) → demo CaCl2(aq) + AgNO3(aq) → Na2SO4(aq) + BaBr2(aq) →

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E. Combustion Reactions (Ch 9.1)

are chemical reactions with oxygen that proceed with the evolution of heat and light: C2H6O + 3 O2 → 2 CO2 + __ H2O ethanol C3H8 + 5 O2 → 3 CO2 + __ H2O propane 2 ZnS + 3 O2 → 2 ZnO + __ SO2

2 Mg + O2 → _________ combustion reaction combination reaction redox reaction

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F. Oxidation – Reduction Reactions (Ch. 9.2 & 9.3) __________ In redox reactions a transfer of electron from one reactant to another occurs. 2 Mg + O2 → ________ oxidation = loss of electrons reduction = gain of electrons

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Assignments of Oxidation Numbers (ox#) 1. In elemental states = _______ Na Cl2 P4 O2 Mg 2. Monatomic ions = charge on the ion Na+ +1 S2- -2 Zn2+ +2 3. H is usually +1 O is usually -2 F is always -1 in compounds

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4. a. The sum of all oxidation numbers in a neutral compound = Zero b. For polyatomic ions the sum = ______________. 5. In binary molecules, the more electronegative element is assigned a negative number equal to its charge in binary ionic compounds. CCl4 Cl has oxidation number (ox#) of -1 ox# C + ox# 4(-1) = 0 ox# C = ____

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Example A: (rules 3 & 4a) P2O5 2(ox# P) + 5(ox# O) = 0 2(ox# P) + 5(-2) = 0 2(ox# P) = _____ ox# P = _____ Oxidation numbers for the elements in P2O5 P = ____ O = -2

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Example B: (rules 2, 3 & 4a) KMnO4 (ox# K) + (ox# Mn) + 4(ox# O) = 0 (+1) + (ox# Mn) + 4(-2) = 0 (ox# Mn) = ___________ Oxidation numbers for the elements in KMnO4 K = +1 Mn = ____ O = -2

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Example C: (rules 3 & 4b) NO3

- (ox# N) + 3(ox# O) = -1 (ox# N) + 3(-2) = -1 (ox# N) = __________ Oxidation numbers for the elements in NO3

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N = ___ O = -2

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Terminology Associated with Redox Processes (Ch 9.3)

2 Mg + O2 → 2 MgO 0 0 +2 -2 oxidation = loss of electrons reduction = gain of electrons Mg is oxidized from 0 to +2 O2 accepts the electrons from Mg O2 oxidizes Mg to Mg2+ O2 is the ____________ agent O2 is reduced from 0 to -2 Mg transfers electrons to O2 Mg reduces O2 to O2- Mg is the ____________ agent

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Practice example: 2 KBr + Cl2 → 2 KCl + Br2 +1 -1 0 +1 -1 0 K = no redox Br = oxidized from -1 to 0 Cl = ____________ agent Cl = reduced from 0 to -1 Br = ____________ agent NOTE: Electron transfer occurs in one direction only!

2 KCl + Br2 → No Reaction Recall order of reactivity: F > Cl > Br > I F2 is the strongest oxidizing agent, it will replace all. I2 is the weakest of the halogens, it will replace none.

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Supplemental Material: Comparing Strength of Agents Recall: Li, Na, K reaction with H2O Order of reactivity: Li < Na < K 2 Na + 2 H2O → 2 NaOH + H2 0 +1 -2 +1 -2 +1 0 Na = strong reducing agent Na+ = weak oxidizing agent Contrast with Ag, Au, Cu + H2O Noble metals do not react, they are weaker reducing agents that alkali metals. Predict the outcomes: Na + AgNO3 → Ag + LiBr →

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Demo: Compare the reactivity of Zn and Fe

Zn is a stronger reducing agent than Fe. It can be used as a ____________ metal to prevent corrosion of iron.

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G. Acid-Base Neutralization Reactions (Ch 10.1, 10.6 & 10.7) Acid + Base → Salt + Water HX + BOH → BX + HOH __________________ reaction

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Arrhenius Acids produce H+ in water

Fig 10.1

Ionization is the process in which cations and anions are produced from a molecule dissolved in water. HCl hydrochloric acid → H+ + Cl- ionization in H2O HNO3 nitric acid HClO4 perchloric acid ______ sulfuric acid H3PO4 phosphoric acid You must know these acids.

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Arrhenius Bases produce OH- in water

Fig 10.1

Dissociation is the process in which cations and anions are released from an ionic compound that is dissolved in water. H2O NaOH(s) Na+(aq) + OH-(aq) Other common bases: KOH _________

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Balancing Neutralization Reactions H3PO4(aq) + NaOH(aq) → unbalanced H3PO4(aq) + NaOH(aq) → Na3PO4(aq) + H2O(l) unbalanced H3PO4(aq) + 3 NaOH(aq) → Na3PO4(aq) + 3 H2O(l) 3H+ + PO4

3- + 3Na+ + 3OH- → 3Na+ + PO43- + 3H2O

Net ionic equation: ______________________

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Figure 10.6 The acid-base reaction between sulfuric acid and barium hydroxide produces the insoluble salt barium sulfate.

Drill Problem: 1. Write the complete, balanced equation for this neutralization, indicating the state of each compound (s), (aq) etc. 2. Write the ionic equation. 3. Identify any spectator ions.