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Chemical Reactions and Equations
Chapter 8
What does a chemical formula represent? The elements contained in a chemical
substance
Indicates the number of atoms of the element just to the right of the element symbol
a whole number that appears in front of a formula in a chemical equation.
What is a subscript? What does it indicate?
What is a coefficient?
Chemical Formulas
2 C8H18
indicates there are 8 Carbon atoms in
the molecule
indicates there are 18 hydrogen atoms
in the molecule
Coefficient means 2
molecules
Visualizing CompoundsExample: H2O
H atoms = ________
O atoms = ________
Model of H2O:
2
1
What is a diatomic element?An element with two atoms when it is by itself
H2 O2 F2 Br2 I2 N2 Cl2
Hydrogen Molecule Oxygen Molecule
DIATOMIC ELEMENTS
You can also mark them off on your periodic table as the SUPER SEVEN!
Chemical Reaction
When bonds are broken and new bonds are formed producing a new substance
Chemical Equation
Symbolizes or represents a chemical reaction
Reactants
Original substances in a chemical reaction
Products
Substances formed in a chemical reaction
REACTANTS yields PRODUCTS
H2 + O2 H2O
Igniting a mixture of hydrogen and oxygen will form water. The symbol equation is:
Reactants Product
How does a chemical reaction occur?
Atoms must collide for the reaction to occur
Atoms are rearranged in a chemical change- None are lost- None are gained
any reaction that gives off heat
Example:
2H2 (g) + O2 (g) 2H2O (l) + heat
Exothermic Reaction
Endothermic Reaction
any reaction in which heat is added
Example:
heat + 2HgO (s) 2Hg (l) + O2 (g)
Evidence of a Chemical Change
1. Color change (THAT YOU DID NOT CAUSE!!)
2. Temperature change3. Odor change4. Formation of a gas5. Formation of a precipitate
precipitate: insoluble solid that separates out of solution
Balancing Chemical Equations Notes
A Chemical Reaction
Potassium Iodide [KI] Lead Nitrate [Pb(NO3)2]
Final Product
Did a chemical change occur?How do you know?
Is matter conserved in this reaction?
According to the LAW OF CONSERVATION OF MATTER:
the total atoms of reactants must equal the total atoms of products[matter can’t be created or destroyed!]
When you have a chemical reaction, you must add coefficients to balance the
reaction!
Atom Inventory
__H2 + __O2 __H2O
Reactant Side
Product Side
Atom Type
Number of Atoms
Atom Type
Number of Atoms
H H
O O
2
2
2
1
UNBALANCED!
To balance an equation, coefficients CAN be added in front of products or reactants. DO NOT CHANGE SUBSCRIPTS!
New Atom Inventory__H2 + __O2 __H2O
Reactant Side
Product Side
Atom Type
Number of Atoms
Atom Type
Number of Atoms
H H
O O
4
2 2
2
2UNBALANCED!
New Atom Inventory__H2 + __O2 __H2O
Reactant Side
Product Side
Atom Type
Number of Atoms
Atom Type
Number of Atoms
H H
O O
2
4
2 2
2
4BALANCED!
Balancing Equations___ Mg + ___ N2 ---> ___ Mg3N2
___ H2S + ___ Cl2 ---> ___ S8 + ___ HCl
___ Al + ___ HCl ---> ___ AlCl3 + ___ H2
___ Fe2O3 + ___ CO ---> ___ Fe + ___ CO2
Classifying Chemical Reactions
• Two or more reactants combine to form ONE product.
(marriage)
example:
2Mg (s) + O2 (g) 2MgO (s)
A + X AX
Synthesis
• ONE reactant breaks down into smaller parts.
(divorce)
AX A + X
Decomposition
example:
2H2O (l) 2H2 (g) + O2 (g)
• A single element replaces an element that is part of a compound.
example:
2 Al(s) + 3 Fe(NO3)2(aq) 3 Fe(s) + 2 Al(NO3)3(aq)
A + BX B + AX Y + BX X + BY
Single Displacement
• Ions from two different compounds exchange places to form two new compounds.
(wife swap)
AX + BY AY + BX
2KI(aq) + Pb(NO3)2 (aq) PbI2 (s) + 2KNO3 (aq)
Double Displacement
• A compound (usually a hydrocarbon) reacts with oxygen, releasing carbon dioxide and water.
example: combustion of propane
C3H8 (g) + 5O2 (g) 3CO2 (g) + 4H2O (g)
AB + O2 CO2 + H2O
Combustion
Activity Series
What is the activity series?
When elements are ranked in order of their relative reactivities
Activity Series of the Elements
1.Why is sodium not used for silverware?
It is highly reactive and reacts with water.
2. Why has so much gold 2. Why has so much gold jewelry survived from ancient jewelry survived from ancient civilizations?civilizations?
It is unreactive with oxygen or water and therefore does not readily break down.
3. Why is food canned in containers made from steel coated with a thin layer of tin?Steel makes a strong container and the tin lining does not react with the contents.
4. Why are cars painted?
To prevent the iron from rusting by being exposed to oxygen in air.
Writing Chemical Reactions Notes
word equation: equation in which the reactants and products in a chemical reaction are represented by words
a word equation is qualitative
example:
methane + oxygen carbon dioxide + water
Word Equations
formula equation: represents the reactants and products of a chemical reaction by their symbols or formulas
a formula equation is quantitative
example:
CH4(g) + 2O2(g) CO2(g) + 2H2O(g)
Formula Equations
Symbols in a Chemical Reaction
Writing Chemical Reactions
Steps to writing a reaction:1. Balance the equation.2. Fill in the phases of matter.3. Identify the reaction type.
Example 1Aluminum metal reacts with a solution of
hydrochloric acid to produce hydrogen gas and aluminum chloride solution.
Example 2Magnesium metal burns in oxygen gas to
produce solid magnesium oxide.
Example 3Hydrogen peroxide (H2O2) solution breaks down
to produce oxygen gas and liquid water in the presence of the catalyst “catalase”.
Example 4Iron (III) Chloride solution and sodium hydroxide
solution react to produce solid iron (III) hydroxide and sodium chloride solution.
Example 5A piece of zinc metal is placed in copper (II)
nitrate solution producing copper metal and zinc nitrate solution.
Example 6Copper (II) sulfate solution and sodium
hydroxide solution react to produce solid copper (II) hydroxide and sodium sulfate solution.