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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