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Unit 13:CHEMICAL REACTIONS
Reactants: Zn + I2 Product: Zn I2
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Unit 13 Learning Objectives:
Explore the nature of chemical reactions, including catalysts and reactants.
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Unit 13 Learning Objectives:
Explore the nature of chemical reactions, including catalysts and reactants.
Law of conservation of mass and energy.
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Unit 13 Learning Objectives:
Explore the nature of chemical reactions, including catalysts and reactants.
Law of conservation of mass and energy.
Write and balance chemical equations.
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Unit 13 Learning Objectives:
Explore the nature of chemical reactions, including catalysts and reactants.
Law of conservation of mass and energy.
Write and balance chemical equations.
Learn to classify the different reaction types.
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A Little Review of the Terms
Chemical Reaction: when two or more substances come together to form a NEW substance, this is a chemical reaction!
Substances can be Atoms, Molecules, or Compounds
Reactants
ProductsChemical
reaction is occurring
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A Little Review of the Terms
Chemical Reaction: when two or more substances come together to form a NEW substance, this is a chemical reaction!
Substances can be Atoms, Molecules, or Compounds
Reactants are the things being brought together to react
Products are the new stuff that is made in the reaction!
Reactants
ProductsChemical
reaction is occurring
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Identifying chemical reactions
The release of heat and/or light
The formation of a solid when two liquids are mixed together (precipitate)
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Identifying chemical reactionsThe change in color when two liquids are
poured together
The formation of a gas from a
liquid solution
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Because of the principle of the
conservation of matter
The chemical equation must be balanced
It must have the same number of atoms of the same kind on both sides.
Chemical Equations
C3H8 + O2 CO2 + H2O
C = 3 H = 8 O =2 C = 1 H = 2 O = 3
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Balancing Equations
C3H8 + O2 CO2 + H2O
3C 8HC3H8 + O2 CO2 + H2O
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Balancing Equations
C3H8 + O2 CO2 + H2O
C3H8 + O2 3CO2 + 4H2O
10 O = 6 O + 4 O
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Balancing Equations
C3H8 + O2 CO2 + H2O
C3H8 + O2 3CO2 + 4H2O
10 O
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Balancing Equations
C3H8 + O2 CO2 + H2O
C3H8 + 5O2 3CO2 + 4H2O
10 O
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Which one of the following is a balanced equation?
A. Ca (s) + O2 (g) → 2CaO (s)
B. 2Ca (s) + O2 (g) → 2CaO (s)
C. 3Ca (s) + O2 (g) → CaO (s)
D. 6Ca (s) + O2 (g) → 2CaO (s)
Secret Question
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Which one of the following is a balanced equation?
A. Ca (s) + O2 (g) → 2CaO (s)
B. 2Ca (s) + O2 (g) → 2CaO (s)
C. 3Ca (s) + O2 (g) → CaO (s)
D. 6Ca (s) + O2 (g) → 2CaO (s)
Secret Question
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Which one of the following is a balanced equation?
A. Ca (s) + O2 (g) → 2CaO (s)
B. 2Ca (s) + O2 (g) → 2CaO (s)
C. 3Ca (s) + O2 (g) → CaO (s)
D. 6Ca (s) + O2 (g) → 2CaO (s)
Secret Question
2O 2Ca and 2O2Ca
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• Solid (s)
• Liquid (l)
• Gas (g)
• Aqueous solution (aq)
• Catalyst H2SO4
• Change of temperature () Delta
Symbols Used in Equations
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Chemical Equations
Reactants and Products
Al (s) + O2 (g) ---> Al2O3 (s)
Stoichiometry:
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Chemical Equations
Reactants and Products
Al (s) + O2 (g) ---> Al2O3 (s)
Stoichiometry:
2Al
2
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Chemical Equations
Reactants and Products
Al (s) + O2 (g) ---> Al2O3 (s)
Stoichiometry:
3O
2 times what equals 3?
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Chemical Equations
Reactants and Products
Al (s) + O2 (g) ---> Al2O3 (s)
Stoichiometry:
3O
2 times what equals 3? 1.5
but, that is not a whole number…So, what do we do?
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Chemical Equations
Reactants and Products
Al (s) + O2 (g) ---> 2Al2O3 (s)
Stoichiometry:
6O
2 times what equals 6?
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Chemical Equations
Reactants and Products
Al (s) + 3O2 (g) ---> 2Al2O3 (s)
Stoichiometry:
6O
2 times what equals 6?
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Chemical Equations
Reactants and Products
Al (s) + 3O2 (g) ---> 2Al2O3 (s)
Stoichiometry:
4Al
2 times what equals 6?
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Chemical Equations
Reactants and Products
4 Al (s) + 3 O2 (g) ---> 2 Al2O3 (s)
Stoichiometry: is the part of chemistry that studies amounts of substances that are involved in reactions.
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Chemical EquationsChemical Equations
What happens when you mix rust and aluminum?
Thermite Reaction
Fe2O3 = rust Aluminum powder
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Chemical EquationsChemical Equations
Fe2O3 + 2Al → 2Fe + Al2O3
Thermite Reaction
http://www.youtube.com/watch?v=sjLgzgflCk8&feature=related
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Chemical EquationsChemical Equations
Fe2O3 + 2Al → 2Fe + Al2O3
Thermite Reaction
This reaction needs a lot of heat to get started, but produces far more heat afterwards (> 2000°F)
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Classifying Reactions
• Five main types:
• Synthesis• Combustion• Decomposition• Single displacement• Double displacement
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• Two or more substances combine to form another substance.
– For example: A + B AB
– 2H2 + O2 2H2O
– 2 or more simpler substances one more complex substance
Synthesis Reaction
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Decomposition Reactions• Opposite of synthesis.
– One substance breaks down into 2 or more other substances.
– AB A + B
– One compound 2 or more simpler substances
– 2H2O 2H2 + O2
electricity
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Single Replacement Reaction• One element replaces another element in a compound
– A + BC AC + B
– Element + compound new element + new compound
– Zn + CuSO4 ZnSO4 + Cu
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Double Replacement Reactions• Positive ion of one compound replaces the
positive ion of the other
– AB + CD AD + CB
– 2 compounds 2 new compounds
– Forms precipitate, covalent compound, or gas
AgNO3 (aq) + NaCl (aq) → AgCl (s) + NaNO3 (aq)
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Combustion• Reaction of a substance with oxygen and a flame
– If it is combustion of a hydrocarbon, you always get CO2 and H2O (both gases)
– Oxygen (O2) is always a reactant.
C3H8 + 5 O2 → 3 CO2 + 4 H2O + heat
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