CHEMICAL REACTIONS Reactants: Zn + I2 Product: Zn I2.

CHEMICAL REACTIONS Reactants: Zn + I2 Product: Zn I2

Introduction Chemical reactions occur when bonds (between the electrons of atoms) are formed or broken Chemical reactions involve changes in the chemical composition of matter (the making of new materials with new properties) energy changes Symbols represent elements Formulas describe compounds Chemical equations describe a chemical reaction

Chemical Equations (eqns.)
What is a chemical equation? How do you balance a chemical equation? How do you identify the type of chemical equation?

Chemical Equations A chemical equation is written as an expression similar to a mathematic equation that can be compared to a recipe that a chemist follows in order to produce desired results.

Chemical Equations Their Job: Depict the kind of reactants and products and their relative amounts in a reaction. 4 Al (s) O2 (g) ---> 2 Al2O3 (s) The numbers in the front are called stoichiometric coefficients The letters (s), (g), and (l) are the physical states of compounds.

Chemical Equations Because of the principle of the conservation of matter (matter can not be created or destroyed) an equation must be balanced. It must have the same number of atoms of the same kind on both sides. Law of Conservation of Energy MUST ALSO BE FOLLOWED! Energy changes are written in (endo-/ exothermic reactions) Lavoisier, 1788

Chemical Equations All chemical equations have reactants and products.
All chemical equations have reactants and products. We express a chemical equation as follows: Reactants  Products The arrow is equivalent to an “=“ math. When we describe the equation we use the word “yields” or “produces” instead of equals Example C + O2  CO2 This reads “carbon plus oxygen react to yield carbon dioxide”

Balancing a Chemical Equation
Balancing a Chemical Equation A chemical equation is balanced when the ions or atoms found on the reactant side of the equation equals that found on the product side. The arrow can be considered the balance point.

Symbols Used in Equations
Solid (s) Liquid (l) Gas (g) Aqueous solution (aq) Catalyst H2SO or Pt Escaping gas () Depositing solid (↓) Change of temperature/ heat energy ( or + 3kJ or – 3kJ)

Chemical Reactions and Chemical Equations
Chemical Reactions and Chemical Equations Reactants Products Signs of Driving forces: Color change Formation of a solid/precipitate Evolution of a gas Evolution or absorption of heat In all cases, a more energetically stable (lower energy product) is created

Balancing Equations When balancing a chemical reaction you may add coefficients in front of the compounds to balance the reaction, but you may not change the subscripts. Changing the subscripts changes the compound. Subscripts are determined by the valence electrons (charges for ionic or sharing for covalent) Think back to naming compounds/ determining formulas. NaCl exists, because Na is + and Cl is -, but NaCl2 does NOT exist since you would not have a neutral compound! You can’t just add a number to a formula to balance an equation.

Subscripts vs. Coefficients
The subscripts tell you how many atoms of a particular element are in a compound. The coefficient tells you about the quantity, or number, of molecules of the compound.

Chemical Equations 4 Al(s) + 3 O2(g) ---> 2 Al2O3(s)
4 Al(s) O2(g) > 2 Al2O3(s) This equation means 4 Al atoms + 3 O2 molecules ---produces---> 2 molecules of Al2O3 AND/OR 4 moles of Al + 3 moles of O2 ---produces---> 2 moles of Al2O3

Steps to Balancing Equations
There are four basic steps to balancing a chemical equation. Write the correct formula for the reactants and the products. DO NOT TRY TO BALANCE IT YET! You must write the correct formulas first. **And most importantly, once you write them correctly DO NOT CHANGE THE FORMULAS! Find the number of atoms for each element on the left side. Compare those against the number of the atoms of the same element on the right side. Determine where to place coefficients in front of formulas so that the left side has the same number of atoms as the right side for EACH element in order to balance the equation. Check your answer to see if: The numbers of atoms on both sides of the equation are now balanced. The coefficients are in the lowest possible whole number ratios. (reduced)

Some Suggestions to Help You
Some helpful hints for balancing equations: Take one element at a time, working left to right except for H and O. Metals, then nonmetals are a good way, too. Save H for next to last, and O until last. IF everything balances except for O, and there is no way to balance O with a whole number, double all the coefficients and try again. (Because O is diatomic as an element) (Shortcut) Polyatomic ions that appear on both sides of the equation should be balanced as independent units

Balancing Equations 2 2 ___ H2(g) + ___ O2(g) ---> ___ H2O(l)
___ H2(g) + ___ O2(g) ---> ___ H2O(l) 2 2 What Happened to the Other Oxygen Atom????? This equation is not balanced! Two hydrogen atoms from a hydrogen molecule (H2) combine with one of the oxygen atoms from an oxygen molecule (O2) to form H2O. Then, the remaining oxygen atom combines with two more hydrogen atoms (from another H2 molecule) to make a second H2O molecule.

Balance this equation! Na + Cl2 NaCl Na- 1 Na-1 Cl- 2 Cl-1
Balance this equation! Na + Cl NaCl Na- 1 Na-1 Cl- 2 Cl-1 **note that the number of sodiums balance but the chlorine does not. We will have to use coefficients in order to balance this equation.

Inserting subscripts Na + Cl2 2 NaCl Na- 1 Na- 1 2 Cl- 2 Cl- 1 2
Inserting subscripts Na + Cl NaCl Na- 1 Na- 1 2 Cl- 2 Cl- 1 2 ** Now the chlorine balances but the sodium does not! So we go back and balance the sodium.

Finally balanced! 2Na + Cl2 2 NaCl Na- 1 2 Na-1 2 Cl- 2 Cl-1 2
Finally balanced! 2Na + Cl NaCl Na Na-1 2 Cl- 2 Cl-1 2 **Since the number of each element on the reactant side and the product side of the equation are equal, the equation is balanced.

Balancing Equations 2 3 ___ Al(s) + ___ Br2(l) ---> ___ Al2Br6(s)

Balancing Equations 2 Na3PO4 + Fe2O3 ----> Na2O + FePO4 3 2
Sodium phosphate + iron (III) oxide  sodium oxide + iron (III) phosphate 2 Na3PO Fe2O > Na2O FePO4 3 2

Balancing Equation Practice
Balancing Equation Practice CuCl3 + Li2S  Cu2S3 + LiCl NiNO3 + KCl  NiCl + KNO3 FeCl3 + Na2O  Fe2O3 + NaCl

Answers: 1. 2CuCl3 + 3Li2S  Cu2S3 + 6LiCl
Answers: 1. 2CuCl3 + 3Li2S  Cu2S3 + 6LiCl 2. NiNO3 + KCl  NiCl + KNO3 (already balanced) 3. 2FeCl3 + 3Na2O  Fe2O3 + 6NaCl

Types of Chemical Reactions (rxns.)
Types of Chemical Reactions (rxns.)

Types of Reactions Reactions are classified by their products.
Reactions are classified by their products. There are five types of chemical reactions we will talk about: Synthesis reactions Decomposition reactions Single displacement reactions Double displacement reactions Combustion reactions You need to be able to identify the type of reaction and predict the product(s)

Steps to Writing Reactions
Some steps for doing reactions Identify the type of reaction Predict the product(s) using the type of reaction as a model Balance it Don’t forget about the diatomic elements! (BrINClHOF) For example, Oxygen is O2 as an element. In a compound, it can’t be a diatomic element because it’s not an element anymore, it’s a compound!

Synthesis or Combination reactions
Synthesis (meaning to make) or combination reactions are typified by their single product. If you have a reaction in which at least 2 elements or compounds are reacted and produce a single product, the reaction is a synthesis reaction.

1. Synthesis reactions Synthesis reactions are sometimes called combination or addition reactions. reactant + reactant  1 product Basically: A + B  AB Example: 2H2 + O2  2H2O Example: C + O2  CO2 Note: Single Product! This is your clue that this is a synthesis or combination reaction.

Synthesis Reactions Here is another example of a synthesis reaction

Practice Predict the products. Write and balance the following synthesis reaction equations. Sodium metal reacts with chlorine gas Na(s) + Cl2(g)  Solid Magnesium reacts with fluorine gas Mg(s) + F2(g)  Aluminum metal reacts with fluorine gas Al(s) + F2(g)  2 2 NaCl(s) MgF2(s) Balanced 2 3 2 AlF3(s)

2. Decomposition Reactions
2. Decomposition Reactions Decomposition reactions are really just the opposite of a synthesis reaction. Remember, if you can make a substance, you should be able to break it back apart into its components. A good way to remember decomposition reactions to to remember what happens when something decomposes. It falls apart!

Decomposition Reactions
Decomposition reactions occur when a compound breaks up into the elements or in a few to simpler compounds 1 Reactant  Product + Product Basically: AB  A + B Example: 2 H2O  2H2 + O2 Example: 2 HgO  2Hg + O2 Note: Single Reactant! The single reactant is your clue that this is a decomposition reaction.

Decomposition Reactions
Decomposition Reactions Another view of a decomposition reaction:

Decomposition Exceptions
Decomposition Exceptions Carbonates and chlorates are special case decomposition reactions that do not go to the elements. Carbonates (CO32-) decompose to carbon dioxide and a metal oxide Example: CaCO3  CO2 + CaO Chlorates (ClO3-) decompose to oxygen gas and a metal chloride Example: 2 Al(ClO3)3  2 AlCl3 + 9 O2 There are other special cases, but we will not explore those in this class

Practice Predict the products. Then, write and balance the following decomposition reaction equations: Solid Lead (IV) oxide decomposes PbO2(s)  Aluminum nitride decomposes AlN(s)  Pb(s) + O2(g) 2 2 Al(s) + N2(g)

Practice N2(g) + O2(g)  BaCO3(s)  Co(s)+ S(s)  NH3(g) + H2CO3(aq) 
Identify the type of reaction for each of the following synthesis or decomposition reactions, and write the balanced equation: N2(g) + O2(g)  BaCO3(s)  Co(s)+ S(s)  NH3(g) + H2CO3(aq)  NI3(s)  2 NO (g) BaO(s) + CO2 (g) Co2S3 (s) (NH4)2CO3(s) N2 (g) I2 (s)

3. Single Replacement Reactions
Single replacement reactions occur when one chemical takes the place of another in a reaction. In the typical single replacement reaction, an element trades places with one of the ions in a compound.

Single Replacement Reactions
Single Replacement Reactions occur when one element replaces another in a compound. A metal can replace a metal (+) OR a nonmetal can replace a nonmetal (-). element + compound product + product A + BC  AC + B (if A is a metal) OR A + BC  BA + C (if A is a nonmetal) (remember the cation always goes first!) When H2O splits into ions, it splits into H+ and OH- (not H+ and O-2 !!)

Another view:

The Activity Series Not all single replacement reactions will occur.
Not all single replacement reactions will occur. This depends upon the location of the elements present in the activity series Elements above MAY replace elements below; elements below MAY NOT replace elements above them on the series

You will be given a copy of this!!!!
You will be given a copy of this!!!!

Write and balance the following single replacement reaction equation: Zinc metal reacts with aqueous hydrochloric acid Zn(s) HCl(aq)  ZnCl2 + H2(g) Note: Zinc replaces the hydrogen ion in the reaction [If ZnCl2 + H2(g)  Zn(s) HCl(aq) the reaction WOULD NOT OCCUR because Hydrogen is below zinc on the activity series] 2

Sodium chloride solid reacts with fluorine gas NaCl(s) + F2(g)  NaF(s) + Cl2(g) Note that fluorine replaces chlorine in the compound Aluminum metal reacts with aqueous copper (II) nitrate Al(s)+ Cu(NO3)2(aq) Cu(s) + Al(NO3)3(aq) 2 2 2 3 3 2

4. Double Replacement Reactions
4. Double Replacement Reactions Double replacement reactions are identified by two ions trading places and forming new compounds.

Double Replacement Reactions
Double Replacement Reactions occur when a metal replaces a metal in a compound and a nonmetal replaces a nonmetal in a compound Compound + compound  product + product AB + CD  AD + CB Notice that one ion from compound AB replaces one ion from compound CD.

Double Replacement Reactions
Think about it like “foil”ing in algebra, first and last ions go together + inside ions go together Example: AgNO3(aq) + NaCl(s)  AgCl(s) + NaNO3(aq) Another example: K2SO4(aq) + Ba(NO3)2(aq)  KNO3(aq) + BaSO4(s) 2

If no solid is formed, there is said to be no reaction.
Solubility For a double replacement reaction to have occurred, a solid (precipitate) MUST be formed OR water must be formed in an acid-base reaction. There are rules to determine which of the materials formed is the solid If no solid is formed, there is said to be no reaction.

Figure 8.4: The forming of solid AgCl.

You will be given a copy of this!!!!
Solubility Tables Solubility tables help determine which materials are soluble in water and which are not In general, Solubility Rules can be summarized as follows All compounds containing alkali metal cations and the ammonium ion are soluble. All compounds containing NO3-, ClO4-, ClO3-, and C2H3O2- anions are soluble. All chlorides, bromides, and iodides are soluble except those containing Ag+, Pb2+, or Hg22+. All sulfates are soluble except those containing Hg22+, Pb2+, Sr2+, Ca2+, or Ba2+. All hydroxides are insoluble except compounds of the alkali metals, Ca2+, Sr2+, and Ba2+. All compounds containing PO43-, S2-, CO32-, and SO32- ions are insoluble except those that also contain alkali metals or NH4+. You will be given a copy of this!!!!

Predict the products. Balance the equation
Practice Predict the products. Balance the equation HCl(aq) + AgNO3(aq)  Pb(NO3)2(aq) + BaCl2(aq)  FeCl3(aq) + NaOH(aq)  H2SO4(aq) + NaOH(aq)  HNO3(aq) + AgCl(s) PbCl2(s) + Ba(NO3)2(aq) Fe(OH)3(s) + NaCl(aq) H2O(l) + Na2SO4(aq)

Combustion Reactions Combustion reactions are the ones that burn (or explode!). There are two types of combustion reactions—complete or incomplete reactions. These reactions are identified by their products. They either produce carbon monoxide and water or carbon dioxide and water.

Complete Combustion Reactions
These reactions burn “efficiently” which means they produce carbon dioxide and water. These reactions typically burn cleanly and leave very little residue behind.

5. Combustion Reactions Combustion reactions occur when a hydrocarbon reacts with oxygen gas. This is also called burning!!! In order to burn something you need the 3 things in the “fire triangle”: 1) A Fuel (hydrocarbon) 2) Oxygen to burn it with 3) Something to ignite the reaction (spark)

Combustion Reactions In general: CxHy + O2  CO2 + H2O
In general: CxHy + O2  CO2 + H2O Products in combustion are ALWAYS carbon dioxide and water. (although incomplete burning does cause some by-products like carbon monoxide) Combustion is used to heat homes and run automobiles (octane, as in gasoline, is C8H18)

Complete Combustion Reactions
CH4 + O2  CO2 + H2O They may also be written: CH4  CO2 + H2O (O2 is usually written above the arrow.) Clue: CO2 (carbon dioxide) in the product along with water

Combustion Reactions Edgar Allen Poe’s drooping eyes and mouth are potential signs of CO poisoning.

Combustion Example C5H O2  CO2 + H2O Write the products and balance the following combustion reaction: C10H O2  8 5 6 22 2 31 20 10 CO H2O 11

Incomplete Combustion Reactions
Incomplete Combustion Reactions Incomplete combustion reactions occur when something does not burn efficiently. This can cause a lot of harm if the gases produced cannot escape. Carbon monoxide,an odorless and colorless gas, is dangerous. People poisoned by this gas usually become sleepy and can die due to exposure.

Incomplete Combustion Reactions
Incomplete Combustion Reactions CH4 + O2  CO + H2O These reactions may also be written by: CH4  CO + H2O (the O2 is usually written over the arrow.) Clue: CO (Carbon monoxide as a product.)

Mixed Practice State the type, predict the products, and balance the following reactions: BaCl2 + H2SO4  C6H12 + O2  Zn + CuSO4  Cs + Br2  FeCO3  BaSO4 + HCl CO2 + H2O ZnSO4 + Cu CsBr FeO + CO2

Predicting Products of Reactions
Predicting Products of Reactions Completing reactions requires knowledge of the different reaction types (sometimes called mechanisms). You must first identify the reaction type by the reactants. The only type of reaction that cannot be predicted this way is the combustion reaction since the products are very similar.

First Step: Identify reaction type Example: Al + O2 
First Step: Identify reaction type Example: Al + O2  Clue: 2 elements – Synthesis or combination reaction

Second Step: Write the net ionic equation for the reactants
Second Step: Write the net ionic equation for the reactants Al + O2  becomes Al O2- 

Step 3 Using clues, complete reaction taking care to write each formula correctly by checking charges and “criss-crossing” if necessary. Al + O2  Al3+O2- Al + O2  Al2O3

Predicting Products of Reactions (cont.)
Predicting Products of Reactions (cont.) For Single Replacement reactions, check activity series to make sure the reaction goes. Once you write the molecular equation, you should check for reactants and products that are soluble or insoluble. (Double Replacement only)

Reactions in Aqueous Solutions
Reactions in Aqueous Solutions a.k.a. Net Ionic Equations Molecular Equations: shows complete formulas for reactants and products Does not show what happens on the molecular level Total (or Complete) Ionic Equations: All substances that are strong electrolytes (are soluble and dissociate) are written as their ions. Some ions participate in the reaction Some ions do NOT participate in the reaction-called spectator ions. Net Ionic Equations: show only the ions that participate in the reaction

Writing Total Ionic Equations
Once you write the molecular equation (synthesis, decomposition, etc.), you should check for reactants and products that are soluble or insoluble. We usually assume the reaction is in water We can use a solubility table to tell us what compounds dissolve in water. If the compound is soluble (does dissolve in water), then splits the compound into its component ions If the compound is insoluble (does NOT dissolve in water), then it remains as a compound

Writing Total Ionic Equations
Molecular Equation: K2CrO4 + Pb(NO3)2  PbCrO KNO3 Soluble Soluble Insoluble Soluble Total Ionic Equation: 2 K+ + CrO Pb NO3-  PbCrO4 (s) + 2 K+ + 2 NO3-

Net Ionic Equations These are the same as total ionic equations, but you should cancel out ions that appear on BOTH sides of the equation Total Ionic Equation: 2 K+ + CrO Pb NO3-  PbCrO4 (s) + 2 K+ + 2 NO3- (Spectator ions) Net Ionic Equation: CrO Pb+2  PbCrO4 (s)

Net Ionic Equations Try this one! Write the molecular, total ionic, and net ionic equations for this reaction: Silver nitrate reacts with Lead (II) Chloride in hot water. AgNO3 + PbCl2  Molecular: 2 AgNO3 + PbCl2  2 AgCl + Pb(NO3)2 Total Ionic: 2 Ag+ + 2 NO3- + Pb Cl-  2 AgCl (s) + Pb NO3- Net Ionic: Ag+ + Cl-  AgCl (s)

Acid-Base Reactions Acid: Base:
Acid-Base Reactions Acid: produces hydrogen ions (H+) in solution (Arrhenius) proton donor (Lewis) Base: produces hydroxide ions (OH-) in solution (Arrhenius) proton acceptor (Lewis) The reaction ALWAYS forms water and an ionic compound (sometimes aqueous).

Acid-Base Reactions Example HNO3 (aq) + KOH (aq)  Molecular:
Example HNO3 (aq) + KOH (aq)  Molecular: Total Ionic: H+ (aq) + NO3- (aq) + K+ (aq) + OH- (aq)  H2O (l) + K+ (aq) + NO3- (aq) Net Ionic: H+ (aq) + OH- (aq)  H2O (l) H2O (l) + KNO3 (aq)

Oxidation-Reduction Reactions
a.k.a. Redox Equations Between a metal and a nonmetal forming an ionic compound Electron transfer occurs Oxidation numbers: assigning an excess or deficiency in electrons for each element (the charge based on the compound).

Rules for Oxidation Number (ox. #) Determination
The sum of the oxidation numbers add up to the charge a. all elements have an ox. # of 0 b. ions of elements, ox. # is the charge (Cl-) c. the sum of the ox. # of a complex ion equals the charge (CO3-2 ) H is 1+ when combined with a nonmetal and 1- with a metal H3PO CaH H= 1+ PO4 = Ca = 2+ H= 1-

Rules for Oxidation Numbers (cont.)
Rules for Oxidation Numbers (cont.) F is always 1-; Cl, Br, I are 1- except when combined with each other or O O is 2- except when combined with F (F2O) Group I is 1+ and Group II is 2+ in their compounds

Recognizing Redox Rxns.
Recognizing Redox Rxns. oxidation 2 HCl (aq) + Mg (s)  MgCl2 (aq) + H2 (q) Net: 2 H+ (aq) + Mg2+ (aq)  Mg 2+ (aq) + H2 0 (q) Loss of electron = oxidation Gain of electron = reduction “LEO the lion goes GER" 1+ 2+ reduction

Half Reactions Separate the individual oxidation and reduction reactions. Look at electron movement Half rxn.: Mg0 (aq)  Mg e- 2e- + 2 H+  H20 Net: 2 H+ (aq) + Mg0 (aq)  Mg 2+ (aq) + H2 0 (q) Oxidizing agent: the one reduced (H+) Reducing agent: the one oxidized (Mg0)

Recognition of Redox rxns.
Recognition of Redox rxns. Oxidation # changes Reactions with oxygen Reaction of any element (forms a new compound) Balancing Balance by mass Balance by charge Balance net ionic equation

Fe (s) + Cl2 (aq)  Fe3+ (aq) + Cl- (aq)
Example Problem: Fe (s) + Cl2 (aq)  Fe3+ (aq) + Cl- (aq) Balance by mass Fe (s) + Cl2 (aq)  Fe3+ (aq) Cl- (aq) Write half reaction Fe0 (s)  Fe e- 2e- + Cl2  2 Cl- 2

3. Balance by charge (want # of e- to cancel) (Fe0 (s)  Fe 3+ + 3e-)
3. Balance by charge (want # of e- to cancel) (Fe0 (s)  Fe e-) (2e- + Cl2  2 Cl- ) 2 Fe0 (s) + 6e- + 3Cl2  2 Fe e- + 6 Cl- Final eqn.: 2 Fe (s) + 3Cl2  2 Fe Cl- 2 3 +

Again on types of reactions/ summary/ new ways of looking at it

The Myth! MYTH: Little Mikey (“Mikey Likes It”) from the LIFE cereal commercials in the late 70s died when he ate pop rocks then drank a coke, causing the pop rocks to explode inside his stomach.

The Myth! Not surprisingly, this one is completely false.
The Evidence: Mikey is alive and well. His real name is John Gilchrist and he’s an advertising manager for a New York Radio Station. There isn’t enough carbonation in pop rocks to release more than a tiny amount of CO2 – much less than in a coke. If the myth were true, coke alone should be able to explode your stomach.

Types of Chemical Reactions
We can divide chemical reactions into five basic types. First Type: Synthesis Reaction: Looks like this: A + B AB In this reaction, substance A and substance B “combine” to form a new compound. Substances A and B can be elements in atomic form, elements in molecular form, or compounds.

Examples of Synthesis Reactions
2Na + S Na2S This one is an example of two elements in atomic form (Na and S) combining to form a compound (sodium sulfide). 2H2 + O2 2H2O In this example, A and B are two elements in molecular form (hydrogen and oxygen molecules), and the product is water, which is simply the chemical combination of hydrogen and oxygen.

Examples of Synthesis Reactions
2Fe + O2 2FeO In this example, substance “A” is an element in atomic form (Fe), and substance “B” is an element in molecular form (O2). The result is a direct chemical combination of the two elements (FeO, iron oxide, which is “rust”). CuO + H2O Cu(OH)2 This is an example where both substances going into the reaction are molecules. The result is what you get when you “add” all of the atoms in the reaction together.

Chemical Reactions Second Type: Decomposition Reaction:
Looks like: AB A + B Basically, the opposite of a synthesis reaction. A and B (i.e. the products of the reaction) can be elements (atomic or molecular form), or compounds. Example: 2HgO 2Hg + O2

Chemical Reactions Third Type: Single Replacement
Looks like this: AB + C AC + B As usual, A and B can be elements or compounds, but C is typically an element. Example: 2H2O + 2Na 2NaOH + H2 Here a sodium atom replaces a hydrogen atom in water. The reaction is a bit easier to see if we write water as hydrogen hydroxide and keep the freed hydrogen as an atom: HOH + Na NaOH + H

Chemical Reactions Fourth Type: Double Replacement:
Looks like: AB + CD AD + BC A, B, C, and D can be elements or compounds (they are usually an element or a polyatomic ion). Basically, the atoms (or polyatomic ions) in the reactions “trade partners.”

Chemical Reactions Examples:
Most of our “practice” equations are examples of this type of reaction. 2H3PO4 + 3Mg(OH)2 Mg3(PO4)2 + 6H2O H2SO4 + Mg(OH) MgSO4 + 2H2O

Chemical Reactions Important Type of Double Replacement: Acid-Base Neutralization Reactions An acid: lots of free hydrogen ions (H+). A base: lots of free hydroxide ions (OH-). When you combine the two, the hydrogen ions in the acid combine with the hydroxide ions in the base to make water. The substances that “donated” the hydrogen and hydroxide ions also chemically combine to make a special class of compounds called salts.

Acid-Base Neutralization
Chemically the reaction looks like this: Acid + Base Salt + Water A classic example: HCl + NaOH NaCl + H2O Hydrochloric Acid Water Sodium Hydroxide (Lye) Sodium Chloride (Table Salt)

Acid-Base Neutralization
Here’s the equation again: HCl + NaOH NaCl + H2O Chemically, this is a double replacement reaction: The H traded its Cl for an OH The Na traded its OH for a Cl.

Chemical Reactions Hydrocarbon – A class of compounds formed by combining hydrogen and carbon. Often go by their common names. Examples: CH4 is methane C2H6 is ethane C3H8 is propane C4H10 is butane C8H18 is octane

Chemical Reactions Fifth Type: Combustion Reaction
A hydrocarbon reaction with oxygen. “Complete” combusion: the products are always CO2 and H2O (and a lot of energy in the form of heat and light). “Incomplete” combusion: the products are CO2, H2O, CO, and a “simpler” hydrocarbon (one with fewer carbons).

Combustion Reactions Complete reactions occur when there is plenty of oxygen available for the reaction. Typically hard to ignite. Burn very hot. Incomplete reactions occur when there isn’t enough oxygen available for a “complete” reaction. Easier to ignite. Cooler burning.

Combustion Internal combustion engines (i.e. car engines) typically don’t mix enough oxygen in with the hydrocarbon (gasoline) to support a complete reaction. Result: Leftover hydrocarbons (toxic), and the production of carbon monoxide (very toxic). Both are major contributors to pollution.

Combustion Would letting more “air into the mix” (for a more complete reaction) solve air pollution caused by cars? No! “Hard to ignite” means the car is more prone to flooding and stalling. “Hotter burning” has several detrimental effects: Hard on the engine’s oil. Creates various nitrogen-oxygen compounds that can form powerful acids (e.g. nitric acid), and other very toxic pollutants.

CHEMICAL REACTIONS Reactants: Zn + I2 Product: Zn I2.

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