2/14/11 – “C” day Objective: To assess the concepts of ionic and covalent bonding. Do Now:...
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Transcript of 2/14/11 – “C” day Objective: To assess the concepts of ionic and covalent bonding. Do Now:...
Chemical reactionstypes and balancing
2/14/11 – “C” dayObjective: 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” dayObjective: Introduce the concept of chemical reactions.
Do Now: Balance the following: P4 + O2 P4O6
Today:1. Check in HW2. Check Answers 3. More Balancing
Equations
2/16/11 – “E” dayObjective: 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 O2
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
http://www.youtube.com/watch?v=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
MATTERnumber and type number and type
→ READ as an = sign
HCl + Zn → ZnCl2 + H2
Are there the same number of atoms of each type on each side of the →?
Balancing equations
HCl + Zn → ZnCl2 + H2
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
H 1 → 2
Cl 1 → 2
Zn 1 → 1
Balancing equations
2HCl + Zn → ZnCl2 + H2
Step 3: compare numbers, is it balanced now?
H 2 → 2
Cl 2 → 2
Zn 1 → 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
H2, N2, O2, F2, Cl2, Br2 and I2
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
N2 + 3H2 2NH3
2H2 + O2 2H2O
Decomposition
The opposite of synthesis
One reactant making 2 or more products
AB → A + B
2KClO3 2KCl + 3O2
2Ag2O 4Ag + O2
Single Replacementone 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 + F2 2NaF + Cl2
Na + H2O NaOH + H2
K + MgBr2 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
CaCl2 + Na2SO4 → CaSO4 + 2 NaCl
FeCl2 + K2S FeS + 2KCl
Combustion
Reactants: Carbon and Hydrogen containing compound reacting with oxygen
Product: Carbon dioxide and water
CxHy + O2 CO2 + H2O
Combustion
Examples
CH4 +3O2 → CO2 + 2 H2O
C3H8 + 5O2 3CO2 + 4H2O
Types of reactions
Demonstration Lab
Types of reactions
Types of chemical reactions IF WS
Synthesis – Predicting products
and balancingTwo or more reactants one
product
Examples:
Na + Cl2
2Na + Cl2 2NaCl
Synthesis – Predicting products
and balancingRb + Cl2
Rb + Cl2 RbCl
2Rb + Cl2 2RbCl
K + Cl2
K + Cl2 KCl not balanced
2K + Cl2 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:
H2CO3 CO2 + H2O
Decomposition: one reactant, two (or more products)
Decomposition
Decomposition
Often decomposition requires adding energy.
If you add electricity to water, can make it decompose:
H2O → H2 + O2
2H2O → 2H2 + O2
Balancing Synthesis and Decomposition Reactions WS
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 + CuCl2 AlCl3 + Cu
Balance:
2Al + 3CuCl2 2AlCl3 + 3Cu
Single Replacement
Examples of two nonmetals and one metal
Mg + HCl MgCl2 + H2
Balance
Mg + 2HCl MgCl2 + H2
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.MgBr2 and Cl2
2. KI and F2
Answers
1. Magnesium Bromide and ChlorineMgBr2 + Cl2 . Bromine and Chlorine==> MgCl2 + Br2
2. Potassium Iodide and Fluorine 2KI + F2 Iodine and Fluorine ==> 2KF + I2
Balancing SR reactions WS
SR reactions Lab
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 + AgNO3
KBr + AgNO3 AgBr(s) + KNO3 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:
HNO3 + LiOH
HNO3 + LiOH LiNO3 + H2O balanced
Water formed
Double Replacement
How to predict products:
ID cations
Switch them!
Write proper formulas
Balance
Double replacement lab
Balancing DR WS
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.