2/14/11 – “C” day  Objective: To assess the concepts of ionic and covalent bonding.  Do Now: What property of water is determined by its shape? How do water molecules behave?

2/15/11 – “D” day  Objective: Introduce the concept of chemical reactions.  Do Now: Balance the following:  P 4 + O 2  P 4 O 6 Today: 1.Check in HW 2.Check Answers 3.More Balancing Equations

2/16/11 – “E” day  Objective: To apply law of conservation of mass to chemical reactions.  Do Now: What is the law of conservation of mass? Today: 1.Collect 11.1 Guided Read 2.Chemical Reaction Notes 3.Reaction in a Bag Lab

Chemical reactions  When one or more reactants are changed into one or more products, a chemical reaction has occurred.  The atoms do not change, but are rearranged.

Chemical reactions  The changing of substances into other substances by the breaking of old bonds and the formation of new bonds

Terms to remember  The number in front of a substance is called the coefficient  The coefficient multiplies everything in the substance

Terms to remember  Subscript – the number under an element – for example the 2 in O 2  The subscript tells how many of that type of atom is in a compound

Practice  How many of each type of atom are there in 2 Al2(SO4)3?  4 Al  6S  24 O

Chemical reaction- example  Adding HCl to Zn  =HxiW2iPUZiw&feature=related =HxiW2iPUZiw&feature=related How many safety mistakes can you find?

Mistakes  Goggles?  Gloves? – Really strong HCl  Poor judgment – comment about holding balloon in teeth  Fire/explosion

Zn + HCl  What happened?  How can you tell that a chemical reaction occurred?

Chemical reaction  HCl + Zn → ZnCl2 + H2 The atoms in the products are the same atoms that were in the reactants, they are just arranged differently.

Nomenclature  HCl + Zn → ZnCl2 + H2 Reactants → Products Reactants react to produce products

LAW OF CONSERVATION OF MATTER  number and type  number and type  → READ as an = sign HCl + Zn → ZnCl 2 + H 2 Are there the same number of atoms of each type on each side of the → ?

Balancing equations  HCl + Zn → ZnCl 2 + H 2  Step 1: Count the number of each type of atom on each side  H  Cl  Zn

Balancing equations  HCl + Zn → ZnCl2 + H2  Step 2: compare numbers, what needs to be changed to make them the same H1→2H1→2  Cl1 → 2  Zn 1 → 1

Balancing equations  2HCl + Zn → ZnCl2 + H2  Step 3: compare numbers, is it balanced now? H2→2H2→2  Cl2 → 2  Zn1 → 1

Chemical Reaction 2  H2 + O2 → H2O  Is this balanced?  How would you balance it?

Chemical Reaction 2  2H2 + O2 → 2H2O

Diatomic molecules  7 elements, most of which we will use all the time, exist in nature as diatomic molecules, which means they only exist as a molecule of 2 atoms bonded together

Diatomic molecules  H 2, N 2, O 2, F 2, Cl 2, Br 2 and I 2  Notice that all but H2 form a 7 on the periodic table.  You need to know these.

Practice balancing equations Worksheets

Types of reactions  Chemical reactions can be classified into 5 different types:  Synthesis  Decomposition  Single replacement  Double replacement  Combustion

Synthesis reactions Reactants: either 2 elements OR 2 compounds Product: MUST be a compound USUALLY combination is 2 reactants  1 product A + B → AB

Synthesis reactions Examples N 2 + 3H 2  2NH 3 2H 2 + O 2  2H 2 O

Decomposition The opposite of synthesis One reactant making 2 or more products AB → A + B 2 KClO 3  2KCl + 3O 2 2Ag 2 O  4Ag + O 2

Single Replacement one atom takes the place of another atom in a compound A + BC  B + AC A has replaced B in this reaction

Single Replacement Examples 2NaCl + F 2  2NaF + Cl 2 Na + H 2 O  NaOH + H 2 K + MgBr 2  KBr + Mg

Double Replacement  When (usually) ions in 2 compounds switch places to form 2 new compounds.  AB + CD → AD + BC  Remember, positive charge (metal) is always written first

Examples  CaCl 2 + Na 2 SO 4 → CaSO NaCl  FeCl 2 + K 2 S  FeS + 2KCl

Combustion Reactants: Carbon and Hydrogen containing compound reacting with oxygen Product: Carbon dioxide and water C x H y + O 2  CO 2 + H 2 O

Combustion  Examples  CH 4 +3O 2 → CO H 2 O  C 3 H 8 + 5O 2  3CO 2 + 4H 2 O

Types of reactions  Demonstration Lab

Types of reactions  Types of chemical reactions IF WS

Synthesis – Predicting products and balancing Two or more reactants  one product Examples: Na + Cl 2  2Na + Cl 2  2NaCl

Synthesis – Predicting products and balancing Rb + Cl 2  Rb + Cl 2  RbCl 2Rb + Cl 2  2RbCl K + Cl 2  K + Cl 2  KCl not balanced 2K + Cl 2  2KCl

Decomposition one reactant  two or more products Exact opposite of a synthesis reaction

Decomposition Seltzer water (carbonic acid) decomposes to produce carbon dioxide and water: H 2 CO 3  CO 2 + H 2 O Decomposition: one reactant, two (or more products)

Decomposition

 Often decomposition requires adding energy.  If you add electricity to water, can make it decompose: H 2 O → H 2 + O 2 2H 2 O → 2H 2 + O 2

Single replacement reactions A + BC → B +AC  Two metals and one nonmetal OR AB + C →AC + B  Two nonmetals and one metal

Single replacement

Single Replacement Examples of two metals and one nonmetal Al + CuCl 2  AlCl 3 + Cu Balance: 2Al + 3CuCl 2  2AlCl 3 + 3Cu

Single Replacement Examples of two nonmetals and one metal Mg + HCl  MgCl 2 + H 2  Balance  Mg + 2HCl  MgCl 2 + H 2

Try these SR reactions Use the following steps: Identify which reactants are switching places Determine neutral ratio for new compound Draw reaction arrow and complete reaction 1.MgBr 2 and Cl 2 2. KI and F 2

Answers 1. Magnesium Bromide and Chlorine MgBr 2 + Cl 2. Bromine and Chlorine ==> MgCl 2 + Br 2 2. Potassium Iodide and Fluorine 2KI + F 2 Iodine and Fluorine ==> 2KF + I 2

Double Replacement AB + CD → AD + BC Involves the exchange of positive cations Gas, precipitate or water is produced

DR - remember positive ions are always written first when listing the product METALS are positive ions and NON-METALS are negative ions a positive must join with a negative

Double Replacement Double replacement reactions usually involve 2 solutions that when mixed give a precipitate (solid). Example: KBr + AgNO 3  KBr + AgNO 3  AgBr(s) + KNO 3 balanced Ppt formed

Double replacement – acid and base  A special kind of double replacement reaction is when an acid (H) is mixed with a base (OH). Example: HNO 3 + LiOH  HNO 3 + LiOH  LiNO 3 + H 2 O balanced Water formed

Double Replacement How to predict products:  ID cations  Switch them!  Write proper formulas  Balance

Putting it all together: Predicting Products and Balancing Determine the type of reaction: synthesis, decomposition, s/d replacement, or combustion Make sure elements present on left are present on right Make sure all charges are net zero Balance equation.

Will the reaction occur?  Will a metal replace another in a single replacement reaction?  Table called an activity series ranks metals from most active to least active.

Will the reaction occur?  More active metals will form compounds.  A + BC → B + AC  Reaction occurs only if A is more reactive than B

 What do you notice about these metals?  Why do you think jewelry is made using copper, silver, gold and platinum?

Activity of metals lab

Will the reaction occur?  In double replacement reactions, the reaction will occur if one of the products forms a precipitate, a gas or water.