Transcript Chemistry of Cars unit_7_chemistry_of_cars

Unit 7 Chemistry of Cars
http://www.saskschools.ca/curr_cont
ent/chem30_05/index.htm
Objectives
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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 energy
2. The collision must have the right orientation
• Animation:
http://www.saskschools.ca/curr_content/che
m30_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?
Halogens
F
Cl
Br
I
Activity Series
Single Replacement Reactions
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Single replacement reactions will favor oxidation of more
reactive metals.
• Less reactive metals remain metals.
Examples: % Penny Lab
1. 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?
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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 + Na2O + SiO2
 K2O(s) + 5 Na2O(s) + N2(g) (V=nRT/P)
 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)
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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
moles of solute
Molarity  M 
Liter of solution
Carburator
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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 endon 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&feat
ure=related
Surface Area & Reaction Rate
Fuel Injection
Catalysts
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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
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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_cont
ent/chem30_05/2_kinetics/assignme
nts/assignment3.htm
Solubility
Chart
At higher
temperatures:
•Most solids become
more soluble
•Most gases become
less soluble.
Therefore…
Solids tend to dissolve best when:
o Heated
o Stirred
o Ground into small particles
Liquids tend to dissolve best when:
o The solution is cold
o Pressure is high
“Like Dissolves Like”
Nonpolar solutes dissolve best in nonpolar solvents
Fats
Steroids
Waxes
Benzene
Hexane
Toluene
Polar and ionic solutes dissolve best in polar solvents
Inorganic Salts
Sugars
Water
Small alcohols
Acetic acid
Saturation of Solutions
 A 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 reactions
Precipitation
reactions
Oxidation-Reduction
Reactions
Combustion
Reactions
Synthesis
reactions
(Reactants are
elements.)
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 242
Acid-Base
Reactions
Decomposition
reactions
(Products are
elements.)
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.
+1
+2
+3
-3 -2 -1
Writing Ionic Compound Formulas
Example: Iron (III) chloride
1. Write the formulas for the cation and
anion, including CHARGES!
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.
Fe3+ Cl-
3
Not balanced!
Writing Ionic Compound Formulas
Example: Aluminum sulfide
1. Write the formulas for the cation and
anion, including CHARGES!
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.
3+
Al
2
2S
3
Not balanced!
Writing Ionic Compound Formulas
Example: Ammonium sulfate
1. Write the formulas for the cation and
anion, including CHARGES!
2. Check to see if charges are
balanced.
( NH)4+
3. Balance charges , if necessary, using
subscripts. Use parentheses if you need
more than one of a polyatomic ion.
SO42-
2
Not balanced!
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 chloride
H2O
CaCl2 (s) → Ca 2+ (aq) + 2 Cl 1-(aq)
Overall Ionic Equations
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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 NO31-(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
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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.
Solu
bility
Chart
potassium sulfate and barium nitrate
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Write the possible double replacement reaction.
K2SO4 (aq) + Ba(NO3)2 (aq) → 2KNO3 (?) + BaSO4 (?)
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Identify the precipitate
BaSO4 (s) from solubility rules or double replacement chart.
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Complete the formula equation
K2SO4 (aq) + Ba(NO3)2 (aq) → 2 KNO3 (aq) + BaSO4 (s)
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Write the overall ionic equation
K1+ (aq) + SO42- (aq) + Ba2+ (aq) + NO31-(aq) →
BaSO4 (s) + 2 K1+(aq) + 2NO31-(aq)
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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 equation
4. Write the overall ionic equation
5. 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?
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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 Numbers
In 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.
0
0
1
1
2 Na  Cl 2  2 Na Cl
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 Rules
7. 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 310. SO42-
My name is Leo.
Grr-rrrr…
Leo Ger
“Lose electron  oxidation”
Zn  2e- + Zn2+
“Gain electron  reduction”
2e- + Cu2+  Cu
Oxidation-Reduction Reactions
Any chemical process in which element
undergo changes in oxidation number is an
oxidation-reduction or redox reaction.
0
0
1
1
2 Na  Cl 2  2 Na Cl
Oxidation-Reduction Reactions
• Oxidation processes - reactions in which the atoms
or ions of an element experience an increase in
oxidation state.
Each sodium atom loses one electron:
0
1
Na  Na  e

A species whose oxidation number increases is oxidized.
Oxidation-Reduction Reactions
• Reduction processes – reaction in which the
oxidation state of the element decreases.
Each chlorine atom gains one electron:
0
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1
Cl  e  Cl
A species whose oxidation number decreases is reduced.
LEO says GER :
Lose Electrons = Oxidation
0
1
Na  Na  e

Sodium is oxidized
Gain Electrons = Reduction
0
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1
Cl  e  Cl
Chlorine is reduced
Redox Practice
1 K → K1+
2 Mn2+ → MnO413 S → S2-
4 Fe3+ → Fe2+
More Redox Practice
5. Mg → Mg2+
6. O2 → O27. 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.
1
0
Na  Na  e

Chlorine is reduced – it is the oxidizing agent
0

1
Cl  e  Cl
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 e2 NO3- + 6 e1- + 8 H1+ → 2 NO + 4 H2O
(oxidation)
(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:
1 5 2
1
1
1
1
1 5 2
Ag N O3 (aq)  Na Cl (aq)  Ag Cl ( s)  Na N O3 (aq)
1 2 1
1
6 2
1
6 2
1
2
2 Na O H (aq)  H 2 S O 4 (aq)   Na 2 S O 4 (aq)  H 2 O(l )
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!
LEO
GER
Losing electrons is oxidation
Gaining electrons is reduction
Losing electrons leaves an atom more positive.
Gaining electrons leaves an atom more
negative.
Metals tend to lose electrons easily to become
oxidized and corrode.
Non-metals tend to gain electrons.
Oxygen is famous for it!
Fe0  Fe+3
Cl2  2 Cl-1
2 Fe + 3 Cl2  2 FeCl3
Animation!