Chapter 2 - Chemical Reactions - Weebly

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Unit 1 - Foundations of ChemistryChapter 2 - Chemical ReactionsUnit 1 - Foundations of Chemistry1 / 42

2.1 - Chemical EquationsPhysical and Chemical ChangesPhysical change: A substance changes its physical appearance, but notits composition. Example: All changes of state.Chemical change: A substance is transformed into a chemically differentsubstance. Example: The burning of hydrogen in air.Unit 1 - Foundations of Chemistry2 / 42

2.1 - Chemical EquationsPhysical and Chemical ChangesPhysical change: A substance changes its physical appearance, but notits composition. Example: All changes of state.Chemical change: A substance is transformed into a chemically differentsubstance. Example: The burning of hydrogen in air.Unit 1 - Foundations of Chemistry2 / 42

Indicators of a Chemical ReactionChemical change:Heat and/or light is given offA new colour appearsA gas is producedA solid precipitate (ppt) is formedWatch: Nitric acid copperWatch: Lead nitrate potassium iodideUnit 1 - Foundations of Chemistry3 / 42

Form of a Chemical ReactionHow can we describe a wide range of reactions?Chemical Equations:Reactants ProductsWe further separate both the reactants and the products by a plus sign:Reactant 1 Reactant 2 Product 1 Product 2Unit 1 - Foundations of Chemistry4 / 42

Examples of word equations:iron oxygen iron(III) oxidecopper silver nitrate silver copper(II) nitrateExamples of skeleton equations:Zn HCl H2 ZnCl2heatH2 O2 H2 Oor4H2 O2 H2 OUnit 1 - Foundations of Chemistry5 / 42

Examples: Write skeleton equations for the following reactions:1AgNO3 and NaCl react to form AgCl and NaNO32potassium sulphate reacts with barium nitrate to form potassiumnitrate and barium sulphateUnit 1 - Foundations of Chemistry6 / 42

Indicating the States of Reactants and ProductsThe physical state of each reactant and product is often added to theformulas in balanced equations. We use the symbols (g), (l), (s), and (aq)for gas, liquid, solid, and aqueous (water) solution.Examples:Fe(s) O2(g) Fe2 O3(s)Zn(s) 2 HCl(aq) H2(g) ZnCl2(aq)CH4(g) 2 O2(g) CO2(g) 2 H2 O(g)Unit 1 - Foundations of Chemistry7 / 42

The Law of Conservation of MassIn a chemical reaction, the total mass of the reactants is always equal tothe total mass of the products.What does this imply?Unit 1 - Foundations of Chemistry8 / 42

The Law of Conservation of MassIn a chemical reaction, the total mass of the reactants is always equal tothe total mass of the products.What does this imply?In chemical reactions, the atoms of the reactants are simply rearranged to formthe products.Unit 1 - Foundations of Chemistry8 / 42

2.2 - Balancing Chemical EquationsWhat’s incorrect with the chemical equation below?Fe Cl2 FeCl3Unit 1 - Foundations of Chemistry9 / 42

2.2 - Balancing Chemical EquationsWhat’s incorrect with the chemical equation below?Fe Cl2 FeCl3Problem! - The Law of Conservation of Mass states that the mass of thereactants equals the mass of the products.Unit 1 - Foundations of Chemistry9 / 42

We cannot change the subscripts of the formulas to fix this imbalance, asthis completely changes the compounds. Instead, we must change thenumbers of molecules rather than their formulas.Unit 1 - Foundations of Chemistry10 / 42

We cannot change the subscripts of the formulas to fix this imbalance, asthis completely changes the compounds. Instead, we must change thenumbers of molecules rather than their formulas.Fe Fe Cl2 Cl2 Cl2 FeCl3 FeCl32Fe 3Cl2 2FeCl3Unit 1 - Foundations of Chemistry10 / 42

Steps to balancing chemical equations:1Balance metal elements2Balance non-metal elements excluding hydrogen and oxygen3Balance hydrogen4Balance oxygen5Reduce coefficients if possibleTip! - If any polyatomics are present balance them as one unit. This onlyonly work if it occurs on both sides of the equation.Unit 1 - Foundations of Chemistry11 / 42

Balance the following equations:1Al Br2 AlBr32N2 H2 NH33N2 H 4 4Na H2 O NaOH 5Ca HNO3 H2 6Fe(NO3 )3 O2 H2 O (NH4 )2 CO3 N2H2Ca(NO3 )2Fe2 (CO3 )3 Unit 1 - Foundations of ChemistryNH4 NO312 / 42

2.3 - Types of Chemical ReactionsWe shall investigate five types of chemical le DisplacementUnit 1 - Foundations of Chemistry5Double Displacement13 / 42

Combustions ReactionsA combustion reaction is a reaction of the form:4hydrocarbon oxygen carbon dioxide waterCn H2n 2 O2 CO2 H2 OFor example:2 C4 H10 13 O2 8 CO2 10 H2 O4Demonstration: 2 CH3 OH 3 O2 2 CO2 4 H2 OUnit 1 - Foundations of Chemistry14 / 42

Balancing Combustion ReactionsFor combustion reactions, we usually balance in this order:1Balance carbons2Balance hydrogens3Balance oxygensExamples:1CH4 O2 CO2 H2 O2C2 H5 OH O2 CO2 H2 O3C2 H6 O2 CO2 H2 OUnit 1 - Foundations of Chemistry15 / 42

Synthesis (Combination) ReactionsSynthesis reactions involve the combination of smaller atoms and/ormolecules into larger molecules.Simple synthesis reactions have the following general formula:Unit 1 - Foundations of Chemistry16 / 42

Simple (elements): A B ABSome complex synthesis reactions have the following general formulas:Metal oxide water Metal hydroxide (a base)Ex: K2 O H2 O 2 KOHCaO H2 O Ca(OH)2Non-metal oxide water Non-metal hydride (an acid)Steps:1) Add one oxygen to the non-metal oxide2) This creates a new polyatomic ion. Reference its charge and placethe appropriate amount of hydrogens out front to balance the charges.Ex: CO2 H2 O H2 CO3Unit 1 - Foundations of Chemistry17 / 42

Complete and balance the following:Examples:Practice:1Na Cl2 1Li Br2 2K Cl2 2Mg N2 3Li2 O H2 O 3SO2 H2 O 4SO3 H2 O 4BaO H2 O Unit 1 - Foundations of Chemistry18 / 42

Decomposition ReactionsDecomposition reactions involve the splitting of a large molecule intoelements or smaller molecules.Simple decomposition reactions have the following general formula:Unit 1 - Foundations of Chemistry19 / 42

Simple (elements): AB A BSome complex decomposition reactions have the following generalformulas:Metallic carbonates:MCO3 MO CO2Metallic sulfates:MSO4 MO SO3Metallic hydroxides:MOH MO H2 OMetallic chlorates:MClO3 MCl O2Demonstration: 2 H2 O2 2 H2 O O2Unit 1 - Foundations of Chemistry20 / 42

Complete and balance the following:Examples:Practice:1HgO 1AgCl 2Ca(OH)2 2MgCO3 3CaCO3 3Mg(OH)2 4ZnSO4 4Sr(ClO3 )2 5KClO3 5FeSO4 Unit 1 - Foundations of Chemistry21 / 42

Single Displacement ReactionsSingle displacement reactions are chemical changes where one elementdisplaces or replaces another element from a compound. They have thefollowing general formula:Note: Cations replace cations and anions replace anions!Demonstration: CuCl2 Al Unit 1 - Foundations of Chemistry22 / 42

Examples: Complete and balance the following:1Zn(s) NiCl2(aq) 2Cu(s) AgNO3(aq) 3Na(s) H2 O(l) Unit 1 - Foundations of Chemistry23 / 42

Practice: Complete and balance the following:1Zn(s) CuCl2(aq) 2AuN(aq) Ca(s) 3Ca(s) H2 O(l) Unit 1 - Foundations of Chemistry24 / 42

Double Displacement ReactionsDouble displacement reactions occur when elements in differentcompounds displace each other or exchange places. They have thefollowing general formula:Note: Cations are always written first!Demonstration: CuCl2 Na3 PO4 Unit 1 - Foundations of Chemistry25 / 42

Examples: Complete and balance the following:1CaCl2(aq) Na2 SO4(aq) 2AgNO3(aq) NaI(aq) Unit 1 - Foundations of Chemistry26 / 42

Practice - Complete and balance the following:1MgSO4(aq) NaOH(aq) 2(NH4 )2 SO4(aq) KOH(aq) Unit 1 - Foundations of Chemistry27 / 42

Question 11Classify each of the following reactions as a combustion, synthesis,decomposition, single or double displacement reaction.2Balance the chemical equation.S8 1)Mg 2)NaN3 Na 3)AgNO3 Ni 4)C 2 H6 5)AgNO3 O2 NaCl MgSN2Ni(NO3 )2 CO2 H2 ONaNO3 Unit 1 - Foundations of ChemistryAgAgCl28 / 42

Question 21Predict the products of the following reactions.2Balance the chemical equation.1)CaCO3(s) 2)C3 H8(g) 3)Al(s) 4)MgO(s) 5)K2 SO4(aq) O2(g) HCl(aq) H2 O(l) Ba(NO3 )2(aq) Unit 1 - Foundations of Chemistry29 / 42

The Activity SeriesSingle Displacement reactions don’t always occur, even if the generalform is present.Consider the following reactions:NaCl K KCl NaKCl Na ?Unit 1 - Foundations of Chemistry30 / 42

The Activity SeriesSingle Displacement reactions don’t always occur, even if the generalform is present.Consider the following reactions:NaCl K KCl NaKCl Na ?The last reaction does not occur, because sodium (Na) is less reactivethan potassium (K).Unit 1 - Foundations of Chemistry30 / 42

General Rule: More reactive elements will generally be able to displaceelements that are less reactive.Any element on the table will displace an element below it.Unit 1 - Foundations of Chemistry31 / 42

Example: In which of the following cases will a reaction not occur? Forthe reactions that you predict will occur, complete and balance theequation.1Al(s) H2 O(s) 2Cu(s) Hg(NO3 )2(aq) 3Br2(aq) MgI2(aq) 4Br2(aq) CaCl2(aq) Unit 1 - Foundations of Chemistry32 / 42

Ionic Compounds in WaterExample: Solid NaCl consists of Na and Cl– ions. What happens whenNaCl (table salt) is dissolved in water?Unit 1 - Foundations of Chemistry33 / 42

Ionic Compounds in WaterExample: Solid NaCl consists of Na and Cl– ions. What happens whenNaCl (table salt) is dissolved in water?Unit 1 - Foundations of Chemistry33 / 42

When NaCl dissolves in water, each ion separates from the solid structureand disperses throughout the solution. The ionic solid dissociates into itscomponent ions as it dissolves.Dissociation is the process where ionic compounds dissolve in water andsplit up into their individual ions.Examples:NaCl(s) Ba(NO3 )2(s) Al2 (SO4 )3(s) Unit 1 - Foundations of Chemistry34 / 42

SolubilitySolubility refers to the ability of a compound to dissolve in a solvent. Thecompound being dissolved is called the solute and the liquid doing thedissolving is called the solvent (usually water for ionic compounds).Insolubility refers to a compound’s tendency to remain undissolved in asolvent.Example:Oil waterIced tea waterUnit 1 - Foundations of Chemistry35 / 42

Types of Double Displacement ReactionsThere are three main types of double displacement reactions.1Reactions in which precipitates are formed.2Reactions that produce water.3Reactions that produce a gas.Note: If a precipitate, water, or gas is NOT produced in a doubledisplacement reaction, no reaction has occurred.We’ll only focus on the first two types.Unit 1 - Foundations of Chemistry36 / 42

1) Precipitation ReactionsA precipitate is an insoluble solid formed by a reaction. Reactions thatresult in the formation of an insoluble product are known as precipitationreactions.Example: Pb(NO3 )2(aq) 2 KI(aq) PbI2(s) 2 KNO3(aq)How do we know if a compound will form a precipitate?Unit 1 - Foundations of Chemistry37 / 42

Note: All common ionic compounds of the Group 1 metals and of theammonium ion (NH 4 ) are soluble in water.Unit 1 - Foundations of Chemistry38 / 42

Note: A double displacement reaction will not have occurred if thesolubility rules indicate that:Both products are precipitatesORBoth products are aqueousUnit 1 - Foundations of Chemistry39 / 42

Example: Indicate which of the following double displacement reactionswill go to completion. Indicate the precipitate of the reaction (if any).1Pb(NO3 )2 2Mg(NO3 )2(aq) 3NaOH(aq) HCl NaOH(aq) CaBr2(aq) Unit 1 - Foundations of Chemistry40 / 42

2) Reactions that Produce WaterThis a special type of double displacement reaction. It only occurs whenthe reactants include an acid and a base. This reaction is also known as aneutralization reaction.HA(aq) BOH(aq) BA(aq) H2 O(l)Example:1)HCl(aq) Ba(OH)2(aq) Unit 1 - Foundations of Chemistry41 / 42

Practice: Complete the following double displacement reactions.1H2 SO4(aq) 2HCl(aq) 3H2 SO4(aq) LiOH(aq) NaOH(aq) NH4 OH(aq) Unit 1 - Foundations of Chemistry42 / 42

2.1 - Chemical Equations Physical and Chemical Changes Physical change: A substance changes its physical appearance, but not its composition. Example: All changes of state. Chemical change: A substance is transformed into a chemically di erent substance. Example: The burning of

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