Download - Chemical reactions types and balancing
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Chemical reactionstypes and balancing
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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?
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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
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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
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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.
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Chemical reactions
The changing of substances into other substances by the breaking of old bonds and the formation of new bonds
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Terms to remember
The number in front of a substance is called the coefficient
The coefficient multiplies everything in the substance
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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
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Practice
How many of each type of atom are there in 2 Al2(SO4)3?
4 Al
6S
24 O
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Chemical reaction- example
Adding HCl to Zn
http://www.youtube.com/watch?v=HxiW2iPUZiw&feature=related
How many safety mistakes can you find?
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Mistakes
Goggles?
Gloves? – Really strong HCl
Poor judgment – comment about holding balloon in teeth
Fire/explosion
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Zn + HCl
What happened?
How can you tell that a chemical reaction occurred?
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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.
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Nomenclature
HCl + Zn → ZnCl2 + H2
Reactants → Products
Reactants react to produce products
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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 →?
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Balancing equations
HCl + Zn → ZnCl2 + H2
Step 1: Count the number of each type of atom on each side
H
Cl
Zn
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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
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Balancing equations
2HCl + Zn → ZnCl2 + H2
Step 3: compare numbers, is it balanced now?
H 2 → 2
Cl 2 → 2
Zn 1 → 1
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Chemical Reaction 2
H2 + O2 → H2O
Is this balanced?
How would you balance it?
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Chemical Reaction 2
2H2 + O2 → 2H2O
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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
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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.
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Practice balancing equations
Worksheets
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Types of reactions
Chemical reactions can be classified into 5 different types:
Synthesis Decomposition Single replacement Double replacement Combustion
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Synthesis reactions
Reactants: either 2 elements OR 2 compounds
Product: MUST be a compound
USUALLY combination is
2 reactants 1 product
A + B → AB
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Synthesis reactions
Examples
N2 + 3H2 2NH3
2H2 + O2 2H2O
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Decomposition
The opposite of synthesis
One reactant making 2 or more products
AB → A + B
2KClO3 2KCl + 3O2
2Ag2O 4Ag + O2
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Single Replacementone atom takes the place of another atom
in a compound
A + BC B + AC
A has replaced B in this reaction
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Single Replacement
Examples 2NaCl + F2 2NaF + Cl2
Na + H2O NaOH + H2
K + MgBr2 KBr + Mg
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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
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Examples
CaCl2 + Na2SO4 → CaSO4 + 2 NaCl
FeCl2 + K2S FeS + 2KCl
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Combustion
Reactants: Carbon and Hydrogen containing compound reacting with oxygen
Product: Carbon dioxide and water
CxHy + O2 CO2 + H2O
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Combustion
Examples
CH4 +3O2 → CO2 + 2 H2O
C3H8 + 5O2 3CO2 + 4H2O
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Types of reactions
Demonstration Lab
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Types of reactions
Types of chemical reactions IF WS
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Synthesis – Predicting products
and balancingTwo or more reactants one
product
Examples:
Na + Cl2
2Na + Cl2 2NaCl
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Synthesis – Predicting products
and balancingRb + Cl2
Rb + Cl2 RbCl
2Rb + Cl2 2RbCl
K + Cl2
K + Cl2 KCl not balanced
2K + Cl2 2KCl
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Decomposition
one reactant two or more products
Exact opposite of a synthesis reaction
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Decomposition
Seltzer water (carbonic acid) decomposes to produce carbon
dioxide and water:
H2CO3 CO2 + H2O
Decomposition: one reactant, two (or more products)
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Decomposition
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Decomposition
Often decomposition requires adding energy.
If you add electricity to water, can make it decompose:
H2O → H2 + O2
2H2O → 2H2 + O2
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Balancing Synthesis and Decomposition Reactions WS
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Single replacement reactions
A + BC → B +AC
Two metals and one nonmetal
OR
AB + C →AC + B
Two nonmetals and one metal
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Single replacement
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Single Replacement
Examples of two metals and one nonmetal
Al + CuCl2 AlCl3 + Cu
Balance:
2Al + 3CuCl2 2AlCl3 + 3Cu
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Single Replacement
Examples of two nonmetals and one metal
Mg + HCl MgCl2 + H2
Balance
Mg + 2HCl MgCl2 + H2
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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
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Answers
1. Magnesium Bromide and ChlorineMgBr2 + Cl2 . Bromine and Chlorine==> MgCl2 + Br2
2. Potassium Iodide and Fluorine 2KI + F2 Iodine and Fluorine ==> 2KF + I2
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Balancing SR reactions WS
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SR reactions Lab
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Double Replacement
AB + CD → AD + BC
Involves the exchange of positive cations
Gas, precipitate or water is produced
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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
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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
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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
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Double Replacement
How to predict products:
ID cations
Switch them!
Write proper formulas
Balance
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Double replacement lab
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Balancing DR WS
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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.
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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.
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Will the reaction occur?
More active metals will form compounds.
A + BC → B + AC
Reaction occurs only if A is more reactive than B
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What do you notice about these metals?
Why do you think jewelry is made using copper, silver, gold and platinum?
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Activity of metals lab
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Will the reaction occur?
In double replacement reactions, the reaction will occur if one of the products forms a precipitate, a gas or water.
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