New Unit Energy and Reactions

1. Energy What is energy? Energy = ability to do work What is work? Work = TRANSFER of energy from one object to another.

1. Energy Energy exists in many forms - Kinetic - Potential - Thermal/Heat - Chemical - Electrical - Electromagnetic/Light - Mechanical - Nuclear - Sound

1. Energy IMPORTANT Energy CANNOT be created or destroyed

1. Energy IMPORTANT Energy CANNOT be created or destroyed Energy is CONVERTED from one form to another.

1. Energy IMPORTANT Energy CANNOT be created or destroyed Energy is CONVERTED from one form to another.

1. Energy IMPORTANT Energy CANNOT be created or destroyed Energy is CONVERTED from one form to another.

1. Energy IMPORTANT Energy CANNOT be created or destroyed Energy is CONVERTED from one form to another.

1. Energy In this class: changes in bond energy in reactions and physical changes

1. Energy 1. Explain the conservation of energy 2. Why might a one-step energy conversion be preferred over a two-step conversion?

2. Physical vs Chemical Changes

2. Physical Changes and Reactions How is a physical change different from a chemical change? PhysicalChemical Example: Changing outfitsChanging DNA

2. Physical Changes and Reactions Signs of a chemical change 1. Evolution of a gas 2. Formation of something solid 3. Change in appearance 4. Change in energy

2. Physical Changes and Reactions Both physical and chemical changes need energy or release energy Add energy to ice = water Ice melts = water and releases energy

2. Physical Changes and Reactions Both physical and chemical changes need energy or release energy Add energy to match Match burns = releases energy as fire

2. Physical Changes and Reactions Endo thermic Exo thermic absorbs/needs energyreleases energy

2. Physical Changes and Reactions Show chemical changes with equations Reactants  Products  means “produces”

2. Physical Changes and Reactions Writing Reactions Baking soda, NaHCO 3 combines with acetic acid, HC 2 H 3 O 2 to produce sodium acetate NaC 2 H 3 O 2, carbon dioxide CO 2, and water H 2 O.

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3. Types of Reactions 5 main categories Synthesis Decomposition Combustion Single Replacement Double Replacement

3. Types of Reactions Combustion Explanation: something with carbon + oxygen  Example: C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O Pattern: Carbon + O 2  CO 2 + H 2 O

3. Types of Reactions Synthesis Explanation: when two or more become one Example: H 2 + O 2  2H 2 O Pattern: A + B  AB

3. Types of Reactions Decomposition Explanation: when one becomes two or more/breakup Example: 2H 2 O  H 2 + O 2 Pattern: AB  A + B

3. Types of Reactions Single Replacement Explanation: Love Triangle Example: Zn + CuSO 4  Cu + ZnSO 4 Pattern: A + BC  B + AC

3. Types of Reactions Double Replacement Explanation: Soap Opera Drama Example:KCl+ NaNO 2  NaCl + KNO 2 Pattern: AB + CD  AD + BC

4. Balancing Reactions OBJECTIVE: Applying Conservation of Mass to Reactions

4. Balancing Reactions Conservation of Mass: cannot create or destroy mass this means: there needs to be the same number of atoms on both sides of reaction

4. Balancing Reactions frame + wheels + chain + handlebars + pedals  1 bicycle 1 frame + 2 wheels + 1 chain + 1 handlebar + 2 pedals  1 bicycle What are those numbers? COEFFICIENTS

4. Balancing Reactions H 2 + O 2  H 2 O

4. Balancing Reactions H 2 + O 2  2H 2 O

4. Balancing Reactions 2H 2 + O 2  2H 2 O

4. Balancing Reactions 2H 2 + O 2  2H 2 O NEVER change subscripts

4. Balancing Reactions 2H 2 + O 2  2H 2 O CH 4 + 2O 2  CO 2 + 2H 2 O Cu + 2AgNO 3  2Ag + Cu(NO 3 ) 2 2KI + Pb(NO 3 ) 2  PbI 2 + 2KNO 3 What are those numbers? COEFFICIENTS

4. Balancing Reactions Strategy for Balancing Reactions 1. Start with compound 2. Add coefficients to balance 3. Leave single elements, like O 2, H 2, Al, Cu, etc. for last. 4. Use fractions if necessary. 5. Simplify if necessary. If fractions used, simplify fractions as well. 6. Check work. NEVER CHANGE SUBSCRIPTS! DO NOT SPLIT COMPOUNDS!

A) Identify type of rxnB) Balance 1. Na + O 2  Na 2 O 2 2. Al + S 8  Al 2 S 3 3. O 2 + C 6 H 12 O 6  CO 2 + H 2 O 4. Na + NaNO 3  Na 2 O + N 2 5. H 3 PO 4 + KOH  K 3 PO 4 + H 2 O 6. NH 3 + O 2  N 2 + H 2 O

4. Balancing Reactions Balancing Reactions with Polyatomic Ions Mg + OH -  Mg(OH) 2 HgCl 2 + AgNO 3  Hg(NO 3 ) 2 +AgCl Al + Hg(CH 3 COO) 2  Al(CH 3 COO) 3 + Hg

A) Identify type of rxnB) Balance 1. C 2 H 6 + O 2  CO 2 + H 2 O 2. Al + HAsO 3  H 2 + Al(AsO 3 ) 3 3. H 3 PO 4 + Mg(OH) 2  Mg 3 (PO 4 ) 2 + H 2 O 4. NH 4 OH + H 3 PO 4  (NH 4 ) 3 PO 4 + H 2 O 5. Al(OH) 3 + H 2 SO 4  Al 2 (SO 4 ) 3 + H 2 O 6. C 10 H 22 + O 2  CO 2 + H 2 O (fractions?)

4. Balancing Reactions How are coefficients different from subscripts? 2H 2 + O 2  2H 2 O subscripts = # of atoms

4. Balancing Reactions How are coefficients different from subscripts? 2H 2 + O 2  2H 2 O coefficients = how many

4. Balancing Reactions 2H 2 + O 2  2H 2 O subscripts = # of atoms coefficients = how many

4. Balancing Reactions H 2 + O 2  H 2 O 2 subscripts = # of atoms coefficients = how many

End of Chapter 8 Topics Covered 1. Energy 2. Physical vs. Chemical Changes 3. Types of Reactions 4. Balancing Reactions

Sample Problem Methane, CH 4, reacts with O 2 to combust and produce the following: CO 2 and H 2 O. This reaction results in the release of a large amount of energy. 1. Write a balanced reaction. 2. This is what type of reaction? 3. This reaction resulted in 49.1 grams of CO 2. This is equal to how many moles? 4. CH 4 is a covalent compound. Draw its Lewis Structure