Unit 7 Chemistry of Cars ent/chem30_05/index.htm

Unit 7 Chemistry of Cars

http://www.saskschools.ca/curr_content/chem30_05/index.htm

Objectives• Reaction Rates – Fuel Air Mixtures• Collision Theory – Catalytic Converters• Activity Series (Predicting Single Replacements)• Net Ionic Equations • Solubility & Precipitation (Predicting Double Replacements)• Oxidation & Reduction - Corrosion• Electrochemistry – Car Batteries• Calorimetry – Heat of Fusion & Vaporization• Vapor Pressure & Volatility - Cooling System & Fuels• Boiling Point Elevation & Freezing Point Depression –

Antifreeze• Phase Changes (vs T) (vs P & T) – Air Conditioning

Space Shuttle Propulsion (1 of 3)

• (Essay) Imagine you are a chemical engineer for NASA & you have been assigned the task of changing the rate of reaction in the propulsion systems.

• Describe & explain two changes that you might try. For each suggestion, specify the chemical formula you will adjust, tell how it should change the reaction rate, & explain how this works according to collision theory. (Please complete the essay on the back of the exam.)

Space Shuttle Propulsion (2 of 3)

• In the Space Shuttle rockets, there are two propulsion systems, the liquid propellants, & the solid propellant. T

• he liquid propellant is composed of liquid hydrogen & liquid oxygen which are evaporated & mixed to react as gases and form water vapor according to the following equation: 2H2(g) + O2(g) 2H2O(g).

Space Shuttle Propulsion (3 of 3)

• The solid propellant uses powdered aluminum metal as a fuel reacting with ammonium perchlorate as the oxidizer according to the following equation:

• Al(s) + NH4ClO4(s) Al2O3(s) + HCl(g) + NO2(g) + H2O(g). This reaction is controlled by the presence of the catalyst Fe2O3(s).

4 Stroke Engine

Whoosh!http://www.youtube.com/watch?v=-O1xbx5hffU&feature=related

Internal Combustion Engines• Four-stroke cycle • 1. Induction (intake)

P1V1=P2V2• 2. compression (ignition)

V1/T1 = V2/T2• 3. (expansion) power PV=nRT• 2C8H18(g) + 25O2(g) 16CO2(g) +

18H2O(g) + 10,900kJ

• 4. exhaust – to catalytic converter

Collision Theory

• In order for a reaction to occur the molecules must come in contact by a collision.

• To be successful :1.the collision must have enough energy2.The collision must have the right orientation• Animation:

http://www.saskschools.ca/curr_content/chem30_05/2_kinetics/kinetics2_1.htm

Energy Diagrams• An energy diagram shows

the potential energy of the reactants on the left, the products on the right and the activation energy barrier in the middle.

• If the products have lower energy the reaction will release energy and be exothermic.

• If the products have higher energy the reaction requires energy to be absorbed and is therefore endothermic.

Five Factors Affecting Rates of Reactions

A. Nature of Reactants – reactants vary in stability of electron configurations and bonds.

Examples: Liquids vary in flammability & metals vary in how reactive they are to acids.

Activity Series of Metals•Less reactive metals hold their electrons tighter!•What metals are cars made of? How are they protected?

FClBrI

Halogens

Activity Series Single Replacement Reactions

• Single replacement reactions will favor oxidation of more reactive metals.

• Less reactive metals remain metals.Examples: % Penny Lab1. Zn + H+Cl-

Zn+2Cl-2 + H2

2. Cu + H+Cl- no reaction

3. Mg + Pb+2Cl-12

Pb + Mg+2Cl-2

9F Single Replacement Reactions?• lead + zinc acetate →• iron + aluminum oxide →• silver nitrate + nickel →• sodium bromide + iodine →• aluminum bromide + chlorine →• sodium iodide + bromine →• calcium + hydrochloric acid →• magnesium + nitric acid →• silver + sulfuric acid →• potassium + water →• sodium + water →

Auto Air Bag (1 of 4)• When a sensor in

the car detects a strong front-end collision, it sends an electric current to a wire.

• The wire heats up, and the charge in the inflator undergoes a chemical reaction, producing a gas that rapidly inflates the bag.

Auto Air Bags (2 of 4)• Airbag chemistry• Sodium azide (NaN3) reacts to create sodium metal and N2

gas. • Other chemicals added to 'neutralize' sodium • 2 NaN3(s) 2 Na(s) + 3 N2(g) (V=nRT/P)

• Neutralizations:• 10Na(s) + 2 KNO3(s) K2O(s) + 5 Na2O(s) + N2(g) (V=nRT/P)

• K2O + Na2O + SiO2 Na2K2SiO4 (glass)

Auto Air Bags (3 of 4)

• Sodium Azide• Very toxic compound. (More toxic than

cyanide) • While some of this might escape during

deployment, a more serious concern is what this chemical is doing in junkyards.

• Recycling or controlled deployment would solve problem.

• Currently unregulated.

Auto Air Bags (4 of 4)

• Deployment Details• Air bag volume is » 70 L • Requires » 130 grams of sodium azide. • Full deployment in approximately 0.03

seconds • Velocity of airbag typically close to 200 mph

during inflation • Calculate the rate of reaction:

Temperature• The higher the temperature, the

faster the reaction. • Increasing the temperature 10C,

generally doubles the speed of a reaction.

• Higher temperatures mean faster moving molecules.

• Faster molecules collide more frequently.

• More molecules have enough energy to have successful collisions that react.

• Example: Foods rot quickly in warm climates, but remain good to eat if kept in the fridge.

Concentration

• The higher the concentration, the faster the reaction.

• Higher concentration means more reactant molecules are present and available to react.

• Reactant molecules will collide more frequently since more are near at hand.

• Example: 5% acetic acid is sour vinegar, 100% acetic acid is dangerous

Calculations of Solution Concentration

Molarity - the ratio of moles of solute to liters of solution

solutionofLiter

soluteofmolesMMolarity

Carburator• A carburetor basically consists of an open pipe, a

"throat" or "barrel" through which the air passes into the inlet manifold of the engine. The pipe is in the form of a venturi: it narrows in section and then widens again, causing the airflow to increase in speed in the narrowest part. Below the venturi is a butterfly valve called the throttle valve — a rotating disc that can be turned end-on to the airflow, so as to hardly restrict the flow at all, or can be rotated so that it (almost) completely blocks the flow of air. This valve controls the flow of air through the carburetor throat and thus the quantity of air/fuel mixture the system will deliver, thereby regulating engine power and speed. The throttle is connected, usually through a cable or a mechanical linkage of rods and joints or rarely by pneumatic link, to the accelerator pedal on a car or the equivalent control on other vehicles or equipment.

• Fuel is introduced into the air stream through small holes at the narrowest part of the venturi. Fuel flow in response to a particular pressure drop in the venturi is adjusted by means of precisely-calibrated orifices, referred to as jets, in the fuel path.

Surface Area• Compare a cube with 2cm sides to the same cube cut

into cubes of only 1cm sides. Which has the most surface area?

• More surface area results in faster reactions.• More surface area exposed allows reactants to come in

contact faster. • Atoms in the center of smaller particles take less time

to get to.• Example: aluminum metal is unreactive, aluminum

dust is explosive• http://www.youtube.com/watch?

v=srKewy69Pdk&feature=related

Surface Area & Reaction Rate

Fuel Injection

Catalysts• Catalysts speed up reactions.• Catalysts don’t get used up by the

reaction.• Catalysts lower the activation energy

needed to change from reactants to products.

• Catalysts may bring reactant molecules close together.

• Catalysts may help reactant molecules get oriented the right way.

• Catalysts may prime molecules to react by shifting their electrons more favorable to new bonding combinations.

• Example: Enzymes in your saliva and stomach break down food.

• http://www.youtube.com/watch?v=W0xOgfBaERc&feature=related

Catalytic Converter

• The Reduction Catalyst:• The reduction catalyst is the first stage of the catalytic converter. It uses platinum and

rhodium to help reduce the NOx emissions. When an NO or NO2 molecule contacts the catalyst, the catalyst rips the nitrogen atom out of the molecule and holds on to it, freeing the oxygen in the form of O2. The nitrogen atoms bond with other nitrogen atoms that are also stuck to the catalyst, forming N2.

• Oxidation Catalysts:• Palladium (Pd) and platinum (Pt) metals in very small amounts convert the hydrocarbons of

unburned gasoline and carbon monoxide to carbon dioxide and water. This catalyst aids the reaction of the CO and hydrocarbons with the remaining oxygen in the exhaust gas. But where did this oxygen come from?

Chemical Kinetics Assignment

http://www.saskschools.ca/curr_content/

chem30_05/2_kinetics/assignments/assignment3.htm

Solubility Solubility ChartChart

At higher temperatures:•Most solids become more soluble•Most gases become less soluble.

Therefore…Solids tend to dissolve best when:

o Heatedo Stirredo Ground into small particles

Liquids tend to dissolve best when:

o The solution is coldo Pressure is high

“Like Dissolves Like”

Fats Benzene

Steroids Hexane

Waxes ToluenePolar and ionic solutes dissolve best in polar solvents

Nonpolar solutes dissolve best in nonpolar solvents

Inorganic Salts Water

Sugars Small alcohols

Acetic acid

Saturation of SolutionsA solution that contains the maximum amount

of solute that may be dissolved under existing conditions is saturated.

A solution that contains less solute than a saturated solution under existing conditions is unsaturated.

A solution that contains more dissolved solute than a saturated solution under the same conditions is supersaturated.

Summary of Classes of Reactions

Chemical reactionsChemical reactions

Precipitation reactions

Precipitation reactions

Acid-BaseReactionsAcid-BaseReactions

Oxidation-ReductionReactions

Oxidation-ReductionReactions

Combustion Reactions

Combustion Reactions

Decomposition reactions

(Products are elements.)

Decomposition reactions

(Products are elements.)

Synthesis reactions

(Reactants are elements.)

Synthesis reactions

(Reactants are elements.)

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 242

Ionic Solutions

Ionic Compounds• Ionic Bonds – result from the electrical

attraction between large numbers of cations and anions.– cation – positive ion (loss of electrons)– anion – negative ion (gain electrons)

• Ionic compounds - positive and negative ions that combine to have a neutral charge.

+2

+1

+3 -3 -2 -1

Writing Ionic Compound Formulas

Example: Iron (III) chloride

1. Write the formulas for the cation and anion, including CHARGES! FeFe3+3+ ClCl--2. Check to see if charges are balanced.

3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion.

Not balanced!

33

Writing Ionic Compound Formulas

Example: Aluminum sulfide

1. Write the formulas for the cation and anion, including CHARGES!

AlAl3+3+ SS2-2-2. Check to see if charges are balanced.

3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion.

Not balanced!

22 33

Writing Ionic Compound Formulas

Example: Ammonium sulfate

1. Write the formulas for the cation and anion, including CHARGES!

NHNH44++ SOSO44

2-2-2. Check to see if charges are balanced.

3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion.

Not balanced!

( )( )22

Ionic Compounds in Water

• Dissociation – the separation of ions that occur when an ionic compound dissolves.

NaCl (aq) →

Na1+ + Cl1-

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf

Dissociation

Example: dissociation of sodium chloride H2O

NaCl (s) → Na 1+ (aq) + Cl 1-(aq)

Example: dissociation of calcium chlorideH2O

CaCl2 (s) → Ca 2+ (aq) + 2 Cl 1-(aq)

Overall Ionic Equations

• All soluble ionic compounds are shown as dissociated ions in solution.

Example: precipitation of cadmium sulfide Cd(NO3)2 + (NH4)2S → CdS + 2 NH4NO3

Cd2+ (aq) + 2 NO3

1-(aq)

+ 2NH41-

(aq) + S2-(aq)

→ CdS (s) + 2 NO31-

(aq) + 2NH41-

(aq)

Net Ionic Equations

A net ionic equation includes only those compounds and ions that undergo a chemical change in a reaction in an aqueous solution.

precipitation of cadmium sulfide Cd2+

(aq) + S2-(aq) → CdS (s)

Spectator ions are ions that do not take part in a chemical reaction and are found in solution before and after the reaction.

Solubility & Precipitation Reactions

• Ionic combinations may be soluble (s), slightly soluble (ss) or insoluble (i)

• Double replacement precipitation reactions will only occur if they can form slightly soluble (ss) or insoluble (i) combinations.

Solubility Chart

potassium sulfate and barium nitrate• Write the possible double replacement reaction.

K2SO4 (aq) + Ba(NO3)2 (aq) → 2KNO3 (?) + BaSO4 (?)

• Identify the precipitate

BaSO4 (s) from solubility rules or double replacement chart.

• Complete the formula equation

K2SO4 (aq) + Ba(NO3)2 (aq) → 2 KNO3 (aq) + BaSO4 (s)

• Write the overall ionic equation

• K1+ (aq) + SO42- (aq) + Ba2+ (aq) + NO3

1-(aq) →

BaSO4 (s) + 2 K1+(aq) + 2NO3

1-

(aq)

• Net ionic equation

• Ba2+ (aq + SO42- (aq) → BaSO4 (s)

Ionic Equation Problems

1. Write the possible double replacement reaction.

2. Identify the slightly soluble or insoluble precipitate

3. Complete the formula equation4. Write the overall ionic equation5. Net ionic equation

Nickel II chloride and ammonium sulfide

1. Write the possible double replacement reaction.

2. Identify the precipitate

3. Complete the formula equation

4. Write the overall ionic equation

5. Net ionic equation

9G Double Replacement Reactions?

• aluminum iodide + mercury(II) chloride →• silver (I) nitrate + potassium phosphate →• copper(II) bromide + aluminum chloride →• calcium acetate + sodium carbonate →• ammonium chloride + mercury(I) acetate →• calcium nitrate + hydrochloric acid →• iron(II) sulfide + hydrochloric acid →• copper(II) hydroxide + acetic acid →• calcium hydroxide + phosphoric acid →• calcium bromide + potassium hydroxide →

DMA - February 26, 2008

• Dissociate the following compounds in water– FeCl3

– Ca(OH)2

• Write the overall ionic and net ionic equations:– NaOH (aq) + Mg(NO3)2 →

– K2CO3 (aq) + MgCl2 (aq) →

Oxidation-Reduction

Oxidation-Reduction Reactions

Oxidation NumbersIn order to indicate the general distribution of

electrons among the bonded atoms in a molecular compound or polyatomic ion, oxidation numbers or oxidation states are assigned to the atoms composing the compound or ion. Unlike ionic charges, oxidation numbers do not have an exact physical meaning.

Oxidation Rules

1. The oxidation number of any uncombined element is zero.

The oxidation number of K(s) is 0.

2. The oxidation number of a monatomic ion equals its charge.

11

2

00

22

ClNaClNa

Oxidation Rules

3. The more electronegative element in a binary compound is assigned a number equal to its ion’s charge.

The oxidation number of O in NO is -2.

4. The oxidation number of fluorine is always -1.

Oxidation Rules

5. The oxidation number of oxygen in compounds is -2 unless it F (+2) or it is a peroxide (H2O2 where it is -1)

6. The oxidation number of hydrogen in compounds is +1 unless it is combined with a metal (-1).

The oxidation number of H in LiH is -1.

Oxidation Rules7. The sum of the oxidation numbers in the formula of

a compound is 0.

The oxidation number of C in CaCO3 is +4.

8. The sum of the oxidation numbers in the formula of a polyatomic ion is equal to its charge.

The oxidation number of P in H2PO41- is +5.

(charge -1; hydrogen = 2 x +1; oxygen = 4 x -2; phosphorus = +5)

Oxidation State

1. UF6

2. P4O10

3. CF4

4. HClO3

5. HNO3

Oxidation State

6. N2O5

7. SO2

8. H2SO4

9. PO4 3-

10. SO42-

Leo Ger

“Lose electron oxidation” Zn 2e- + Zn2+

“Gain electron reduction”2e- + Cu2+ Cu

My name is Leo. Grr-rrrr…

Oxidation-Reduction Reactions

11

2

00

22

ClNaClNa

Any chemical process in which element undergo changes in oxidation number is an oxidation-reduction or redox reaction.

Oxidation-Reduction Reactions

Each sodium atom loses one electron:

A species whose oxidation number increases is oxidized.

eNaNa10

• Oxidation processes - reactions in which the atoms or ions of an element experience an increase in oxidation state.

Oxidation-Reduction Reactions

Each chlorine atom gains one electron:

A species whose oxidation number decreases is reduced.

10 CleCl

• Reduction processes – reaction in which the oxidation state of the element decreases.

LEO says GER :

eNaNa10

Lose Electrons = Oxidation

Sodium is oxidized

Gain Electrons = Reduction

10 CleCl Chlorine is reduced

Redox Practice

1 K → K1+

2 Mn2+ → MnO41-

3 S → S2-

4 Fe3+ → Fe2+

More Redox Practice

5. Mg → Mg2+

6. O2 → O2-

7. F1- → F2

8. H2 → H1+

Reducing Agents and Oxidizing Agents

• A reducing agent is a substance that has the potential to cause another substance to be reduced.

• An oxidizing agent is a substance that has the potential to cause another substance to be oxidized.

– The substance reduced is the oxidizing agent.

– The substance oxidized is the reducing agent.

Reducing Agents and Oxidizing Agents

• Sodium is oxidized – it is the reducing agent.

Chlorine is reduced – it is the oxidizing agent

10 CleCl

eNaNa10

Half-reactions

• The part of the reaction involving oxidation or reduction alone can be written as a half-reaction. The overall equation for a redox reaction is the sum of two half-reactions.

3 Cu → 3 Cu2+ + 6 e- (oxidation)

2 NO3- + 6 e1- + 8 H1+ → 2 NO + 4 H2O (reduction)

3 Cu + 2 NO31- + 8 H1+ → 3 CU2+ + 2 NO + 4 H2O

Not All Reactions are Redox Reactions

Reactions in which there has been no change in oxidation number are not redox reactions.

Examples:

)()()()( 3

2511111

3

251

aqONNasClAgaqClNaaqONAg

)()()()(22

2

1

4

26

2

1

4

26

2

1121

lOHaqOSNaaqOSHaqHONa

Redox Reaction Practice

1 2 Na + Cl2 → 2 NaCl

2 C + O2 → CO2

3 2 H2O → 2 H2 + O2

4 NaCl + AgNO3 → AgCl + NaNO3

Practice

5. 2 KClO3 → 2 KCl + 3 O2

6. H2 + Cl2 → 2 HCl

7. H2SO4 + 2 KOH → K2SO4 + H2O

8. Zn + CuSO4 → ZnSO4 + Cu

Trends in Oxidation and Reduction

Active metals: Lose electrons easily Are easily oxidized Are strong reducing agents

Active nonmetals: Gain electrons easily Are easily reduced Are strong oxidizing agents

Redox – Leo says Ger!

Cl2 2 Cl-1Fe0 Fe+3

Non-metals tend to gain electrons.Oxygen is famous for it!

Metals tend to lose electrons easily to become oxidized and corrode.

Gaining electrons leaves an atom more negative.

Losing electrons leaves an atom more positive.

Gaining electrons is reductionLosing electrons is oxidation

GERLEO

2 Fe + 3 Cl2 2 FeCl3

Animation!