6.1 Energy Changes and 6.1 Energy Changes and Chemical ReactionsChemical Reactions

All reactions release or absorb All reactions release or absorb energy.energy.

Common forms of energy are: heat, Common forms of energy are: heat, light, electricity, soundlight, electricity, sound

Energy is stored in the bonds of Energy is stored in the bonds of compounds.compounds.

Breaking a bond requires energy.Breaking a bond requires energy. Bonding releases energy.Bonding releases energy.

The difference between the amount of The difference between the amount of energy absorbed in breaking the bonds in energy absorbed in breaking the bonds in reactants and the amount of energy reactants and the amount of energy released in forming bonds determines released in forming bonds determines whether the reaction is whether the reaction is exoexothermic or thermic or endoendothermic.thermic.

Reactions which need more energy to break Reactions which need more energy to break bonds than they make when bonds are bonds than they make when bonds are formed are formed are endoendothermic (thermic (require heatrequire heat).).

Reactions that make more energy as bonds Reactions that make more energy as bonds form than is needed to break the bonds in form than is needed to break the bonds in the reactants are the reactants are exoexothermic (thermic (give off give off heatheat).).

ExothermicExothermic Endothermic Endothermic

HeatHeat releasedreleased Heat Heat addedadded

Even though Even though energy comes out, energy comes out, a “push” is often a “push” is often needed. needed.

Need a continuous Need a continuous input of energy to input of energy to react react

Reactants Reactants Products + Products + energyenergy

energyenergy + + Reactants Reactants ProductsProducts

Example: burning Example: burning a fuel, an a fuel, an explosion explosion

Vaporizing water, Vaporizing water, cold packcold pack

Consider the following:Consider the following:

It is easier (requires less energy) to It is easier (requires less energy) to build small stable compounds.build small stable compounds.

It is harder (requires more energy) to It is harder (requires more energy) to build large unstable compounds.build large unstable compounds.

Explosives are typically large, Explosives are typically large, unstable compounds that form small unstable compounds that form small stable compounds when they react.stable compounds when they react.

The leftover energy drives the The leftover energy drives the explosion. explosion.

TNT (Trinitrotoluene)TNT (Trinitrotoluene)

CC66HH22(CH(CH33)(NO)(NO33))22(s) (s) ++ O O22(g) (g) →→ CO CO22(g) (g) ++ H H22O(g) O(g) ++ N N22(g)(g)

Very complex, unstable compoundVery complex, unstable compound simple, stable simple, stable compounds compounds

Lots of E required to break the reactant bondLots of E required to break the reactant bond Little energy required to make product bondsLittle energy required to make product bonds Leftover E drives the explosion Leftover E drives the explosion

Law of Conservation of Law of Conservation of EnergyEnergy

Energy cannot be created or Energy cannot be created or destroyed. It can only be changed destroyed. It can only be changed from one form to another.from one form to another.

Example:Example: Burning WoodBurning WoodReactantsReactants ProductsProducts

Chemical energy in wood Chemical energy in wood heat energy heat energy

chemical energychemical energy

radiant energyradiant energy

sound energysound energy

Magic Wand DemonstrationMagic Wand Demonstration Read pages 180 - 182Read pages 180 - 182 Assignment: Assignment: p 185 #1 – 5d & BLM do sheet 6-1, p 185 #1 – 5d & BLM do sheet 6-1,

read 6-2 and do 6-4read 6-2 and do 6-4 6-3 may be done as a bonus 6-3 may be done as a bonus

assignmentassignment

6.2 Synthesis and 6.2 Synthesis and Decomposition ReactionsDecomposition Reactions

Synthesis ReactionSynthesis Reaction – synthesis – synthesis means to make or blend – these means to make or blend – these chemical reactions have several small chemical reactions have several small reactants combining to form larger reactants combining to form larger products.products.

General Form: If A is an element, and General Form: If A is an element, and X is an element we would have:X is an element we would have:

A + X A + X AX AX

Example:Example:

When pop is made:When pop is made:

COCO22(g) + H(g) + H22O(l) O(l) HH22COCO33(aq)(aq)

Decomposition Reaction Decomposition Reaction

Decompose means to break down. Decompose means to break down. These chemical reactions begin with These chemical reactions begin with

larger reactant(s) which break down larger reactant(s) which break down into simpler products. into simpler products.

General From:General From: AX AX A + XA + X

Example:Example: When you open up the pop can:When you open up the pop can:

HH22COCO33(aq)(aq) COCO22(g) + (g) + HH22O(l) O(l)

The COThe CO22 coming out of solution coming out of solution produces the fizz.produces the fizz.

NOTICE the brackets give the state NOTICE the brackets give the state of the substance.of the substance. (s) is solid(s) is solid (l) is liquid(l) is liquid (g) is gas(g) is gas (aq) is aqueous which means dissolved. (aq) is aqueous which means dissolved.

Recall:Recall: A solid takes up little volume,A solid takes up little volume, The same mass of liquid occupies more volume.The same mass of liquid occupies more volume. A same mass of a gas occupies much more A same mass of a gas occupies much more

volume.volume. Recall:Recall:

Materials expand as they get hot.Materials expand as they get hot. Explosions are biggest when the reaction Explosions are biggest when the reaction

can change a material of small volume to a can change a material of small volume to a material with large volume VERY material with large volume VERY QUICKLY.QUICKLY. Rockets, firearms, explosives, etc.Rockets, firearms, explosives, etc.

AssignmentAssignment

Read p 186 – 188Read p 186 – 188 Assignment p 189 #1 – 5Assignment p 189 #1 – 5 BLM sheet 6-5 & 6-6BLM sheet 6-5 & 6-6

6-3 Single and Double 6-3 Single and Double Displacement ReactionsDisplacement Reactions

a chemical reaction in which one a chemical reaction in which one element takes the place of another element takes the place of another element in a compound.element in a compound.

Example: Let A and B be cations. Example: Let A and B be cations. Let X be an anion.Let X be an anion.

A + BX A + BX AX + B AX + B

Think A & B are guys. X is a girl. B Think A & B are guys. X is a girl. B and X are dance partners and have and X are dance partners and have “bonded”. BUT along comes A. Looks “bonded”. BUT along comes A. Looks like A and X bond and B is left alone. like A and X bond and B is left alone.

How could we predict if this would How could we predict if this would happen or not? Well A would have to happen or not? Well A would have to be more “reactive” with X than B was. be more “reactive” with X than B was.

In chemistry the reactivity of elements In chemistry the reactivity of elements has been tested and the results are has been tested and the results are available in reactivity charts called available in reactivity charts called The Activity Series of Metals.The Activity Series of Metals.

Real Life Example:Real Life Example: Mg is more reactive than hydrogen Mg is more reactive than hydrogen

so:so: Mg(s) + HCl(aq) Mg(s) + HCl(aq) MgCl MgCl22(aq)+ (aq)+

HH22(g)(g) Balance the above reaction.Balance the above reaction.

11Mg(s) + Mg(s) + 22HCl(aq) HCl(aq) 11MgCl2(aq)+ MgCl2(aq)+ 11H2(g)H2(g)

Example 2:Example 2: Na is very reactive so:Na is very reactive so: Na(s) + H2O(l) Na(s) + H2O(l) NaOH(aq) + NaOH(aq) +

H2(g)H2(g) Think of water as being ionic Hydrogen Think of water as being ionic Hydrogen

Hydroxide:Hydroxide: Na(s) + H(OH)(l) Na(s) + H(OH)(l) Na(OH)(aq) + Na(OH)(aq) +

H2(g)H2(g) Balance the above reaction.Balance the above reaction. 22Na(s) + Na(s) + 22H(OH)(l) H(OH)(l) 22Na(OH)(aq) + Na(OH)(aq) +

11H2(g)H2(g)

Double Displacement ReactionDouble Displacement Reaction – – a reaction in which the cations from a reaction in which the cations from 2 different compounds exchange 2 different compounds exchange forming 2 new compounds.forming 2 new compounds.

AX + BY AX + BY BX + AY BX + AY Think of 2 couples and the guys Think of 2 couples and the guys

switched places.switched places.

AX + BYAX + BY

Example:Example: 22KI + KI + 11Pb(II)(NOPb(II)(NO33))22 11Pb(II)IPb(II)I22 + +

22K(NOK(NO33)) Notice: an interesting event takes Notice: an interesting event takes

place in the reaction. Two liquids place in the reaction. Two liquids are mixed and one of the materials are mixed and one of the materials produced is a solid. The solid forms produced is a solid. The solid forms as particles that slowly “rain” down as particles that slowly “rain” down to the bottom of the liquid. The solid to the bottom of the liquid. The solid is called a is called a precipitateprecipitate..

Neutralization Neutralization

Neutralization – a double Neutralization – a double displacement reaction that occurs displacement reaction that occurs when an acid and a base are when an acid and a base are combined. The products are always combined. The products are always the same:the same:

Acid + Base Acid + Base Water + Salt Water + Salt A A saltsalt is an ionic compound. is an ionic compound.

Ex)Ex) HNO3 + NaOH HNO3 + NaOH H2O + NaNO3 H2O + NaNO3 (NOTE: it often helps to think of (NOTE: it often helps to think of

H2O as H+OH-)H2O as H+OH-) Read P 190 – 202 and do P 202 1-4, Read P 190 – 202 and do P 202 1-4,

BLM 6-7, 6-8 (read), 6-9 & 6-12 BLM 6-7, 6-8 (read), 6-9 & 6-12

6.4 Organic Chemistry6.4 Organic Chemistry Organic molecules contain Organic molecules contain

carbon (carbon is found in all carbon (carbon is found in all living things).living things).

• Carbon Bonding Carbon Bonding Carbon has 4 valence electronsCarbon has 4 valence electrons

..

.. CC ..

..

Carbon does not form ions, but Carbon does not form ions, but bonds through covalent bonds bonds through covalent bonds (shares e-)(shares e-)

Carbon forms chains with other Carbon forms chains with other carbon atomscarbon atoms

Examples: Methane - CHExamples: Methane - CH44

HX

H XC X HX

H

Ethane – CEthane – C22HH66

Draw the Lewis dot diagram for thisDraw the Lewis dot diagram for this We will use carbon chain drawingsWe will use carbon chain drawings

See boardSee board Carbon chains are most often found Carbon chains are most often found

with hydrogenwith hydrogen

Atoms complete all “open ends” to Atoms complete all “open ends” to the chainsthe chains

Examples: butane (CExamples: butane (C44HH1010) and ) and propane (Cpropane (C33HH88)) Draw theseDraw these

Hydrocarbons (CH) are carbon Hydrocarbons (CH) are carbon chains that contain hydrogenchains that contain hydrogen

Hydrocarbons are very useful fuelsHydrocarbons are very useful fuels

CombustionCombustion Combustion means burningCombustion means burning

Hydrocarbons are excellent fuelsHydrocarbons are excellent fuels When fuels burn they combine with oxygen When fuels burn they combine with oxygen

in exothermic reactionsin exothermic reactions HC + OHC + O22 CO CO22 + H + H22O + Thermal EO + Thermal E

We use the thermal energy:We use the thermal energy: for heatingfor heating to expand gas quickly and we use the force to expand gas quickly and we use the force

produced by the expanding gas (internal produced by the expanding gas (internal combustion engine)combustion engine)

Complete CombustionComplete Combustion

In a perfect world every In a perfect world every hydrocarbon molecule would hydrocarbon molecule would combine with oxygen to produce the combine with oxygen to produce the maximum amount of heat, and only maximum amount of heat, and only COCO22 and H and H22OO

Incomplete CombustionIncomplete Combustion Reactions are often limited by a limited Reactions are often limited by a limited

amount of one of the reactants (Oamount of one of the reactants (O22 or or fuel).fuel).

Incomplete combustion:Incomplete combustion: reduces thermal energyreduces thermal energy wastes fuel (fuel in vehicle exhaust)wastes fuel (fuel in vehicle exhaust) produces Carbon monoxide (CO) which is produces Carbon monoxide (CO) which is

deadly – odorlous, colourless, binds with rec deadly – odorlous, colourless, binds with rec blood cells better than O2 but is not useable blood cells better than O2 but is not useable by the body)by the body)

produces carbon (soot) and causes smog produces carbon (soot) and causes smog and respiratory diseases including cancerand respiratory diseases including cancer

HC + OHC + O22 CO CO22 + H + H22O + CO + C (soot) + O + CO + C (soot) + Reduced Reduced

Thermal E Thermal E

AssignmentAssignment

CYU P 206 1 – 4 & BLM 6-14, 6-15, CYU P 206 1 – 4 & BLM 6-14, 6-15, 6-166-16

Ch 6 ReviewCh 6 Review BLM 6-21BLM 6-21 Ch Review P 209 1-18Ch Review P 209 1-18 Pop Can Canon DemonstrationPop Can Canon Demonstration

Ch 6 - LabCh 6 - Lab

Copper (II) Chloride – CuClCopper (II) Chloride – CuCl22 Sodium Hydroxide – NaOHSodium Hydroxide – NaOHSodium Chloride – NaCl Sodium Chloride – NaCl

Potassium Nitrate – KNOPotassium Nitrate – KNO33

Sodium Carbonate – NaSodium Carbonate – Na22COCO33

Calcium Chloride – CaClCalcium Chloride – CaCl22 Potassium Iodide – KI Potassium Iodide – KI

Lead (II) Nitrate – Pb(NOLead (II) Nitrate – Pb(NO33))22

1.1. HH22 and O and O22 Gas Test Gas Test

a)a) Wooden splint – glows/ignites (2)Wooden splint – glows/ignites (2)

b)b) Lighter – explodes/”pops” (2)Lighter – explodes/”pops” (2)

2.2. Mg and OMg and O22

a)a) Exothermic, flame and light, heat (2)Exothermic, flame and light, heat (2)

b)b) 2Mg + O2Mg + O22 2MgO + thermal E 2MgO + thermal E (4)(4)

c)c) Ionic, metal/non-metal (2)Ionic, metal/non-metal (2)

d)d) 3Mg + N3Mg + N22 = Mg = Mg33NN2 2 + thermal E (4)+ thermal E (4)

3.3. Mg and HClMg and HCla)a) Bubbles and heat (2)Bubbles and heat (2)

b)b) Single displacement, Mg and H switch Single displacement, Mg and H switch places (2)places (2)

c)c) Mg and HCl (1)Mg and HCl (1)

d)d) MgClMgCl22 and H and H2 2 (1)(1)

e)e) Mg + 2HCl = MgClMg + 2HCl = MgCl22 + H + H22 + thermal + thermal E (4)E (4)

4.4. Dble. DisplacementDble. Displacementa)a) Blue precipitate (gelatin) (2)Blue precipitate (gelatin) (2)

b)b) CuClCuCl22 + 2NaOH = Cu(OH) + 2NaOH = Cu(OH)22 + 2NaCl + 2NaCl (4)(4)

c)c) None (2)None (2)

d)d) NaCl + KNONaCl + KNO33 = NR (4) = NR (4)

e)e) Turned foggy/milky, white precipitate Turned foggy/milky, white precipitate (2)(2)

f)f) NaNa22COCO33 + CaCl + CaCl22 = CaCO = CaCO33 + NaCl (4) + NaCl (4)

g)g) Yellow precipitate (2)Yellow precipitate (2)

h)h) 2KI + Pb(NO2KI + Pb(NO33))22 = PbI = PbI22 + 2KNO + 2KNO3 3 (4)(4)