Unit 5 Chemistry Chemical Reactions Acids

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Unit 5 ChemistryChemical Reactions Acids Bases
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• Chemical Equations
• Shorthand representations of chemical reactions.
• -when some chemicals come into contact, they
  break apart, join, or rearrange to form new
  chemicals (always to become more stable)
• Why do we balance equations?
• -Law of conservation of mass
• -atoms are not created or destroyed in a
  chemical reaction, just rearranged to form new
  substances
• Coefficients
• -the number before the chemical formula
• -used to balance chemical equations

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• hydrogen oxygen yields dihydrogen monoxide
• H O ? H2O

2
2
2
2
coefficient
Reactants
Products
yield
1. Diatomic molecules (H O N Cl Br I F)
2. Only 1 oxygen atom out (2 in) ?
place 2 in front of H2O
3. Only 2 hydrogen in (4 out) ? place
2 in front of H2

• Recount total number of each type of atom

Only add coefficients, NEVER ? subscripts
Can you ever make just 1 molecule of water?
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• Steps to Balancing Equations
• 1. Write the formula(s)
• 2. Check for diatomic molecules
• H O N Cl Br I F
• 3. Balance
• A. Polyatomic ions (if same poly. ion
  on both sides ? balance as a chunk)
• B. Metals
• C. Nonmetals
• D. O H
• 4. Recheck your count!!!

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O-2
Na1
OH-1
H2O
Na1

• Sodium hydroxide yields sodium oxide plus water

2
?
NaOH
Na2O
H2O
?




Na




O




H
6
Fe
O
Fe3
O-2

• Iron plus oxygen yields iron (III) oxide

Fe
Fe2O3
?
?
2
2
O
3
2
Fe
O
7
Fe
O
Fe3
O-2

• Iron plus oxygen yields iron (III) oxide

Fe
Fe2O3
?
?
4
2
O
3
2
Fe
O
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Types of Reactions

• 1. Synthesis - usually 1 product
• A B ?? AB
• 2. Decomposition - usually 1 reactant
• AB ? A B
• 3. Single Replacement (single displacement)
• AB C ? AC B
• 4. Double Replacement (double displacement)
• AB CD ? AD CB

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• 2H2 O2 ? 2H2O
• Synthesis (2 R ? 1 P)
• 2NaOH ? Na2O H2O
• Decomposition (1R ? 2 P)
• Na HCl ? H2 NaCl
• Single Replacement
• (elem. compd ? new elem. new compd)
• Ca(OH)2 H2SO4 ? CaSO4 2H2O
• Double Replacement
• (2 compd ? 2 new compd)