Chemical Reactions and Chemical Equations

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Chemical Reactions and Chemical Equations
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Quick ReviewPhysical Change

• A physical change in a substance doesn't change
  what the substance is.
• Example tearing paper, it is still paper

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Chemical Change

• In a chemical change a new substance is formed
  and energy is either given off or absorbed.
• Example burning paper
• The paper is changed into carbon, water, and heat
  is given off.

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Chemical Change

• When substances undergo a chemical change, the
  new substances will have different properties.
• For example Burning wood in a campfire.

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Evidence of a Chemical Change

• Color change
• Light is released
• A solid (precipitate) is produced
• An odor is evident
• Temperature changes
• A gas is given off
• Sound is produced

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Law of Conservation of Matter

• Remember that?
• Matter is NEVER created or destroyed in a
  chemical change. The particles are just
  rearranged to form new substances. The same
  number of particles that existed before the
  change exist after the change!
• Its the law!!!!!

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Chemical Equations

• When writing chemical equations, you MUST follow
  the law of Conservation of Mass.
• There must be the same and kind of atoms on
  each side of the arrow.
• This is referred to as balancing an equation

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Lets Try Some

• H2 O2 H2O
• gas gas
  
  
  liquid
• Balanced?
• Lets balance it
• 2H2 O2 2H2O
• Na Cl NaCl
• soft, reactive metal
  poisonous gas
  
  white solid
• Balanced?
• That is why you see large numbers in front of
  elements and compounds, to balance the of atoms
  on each side of the arrow.

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Types of Chemical Equations

• Synthesis
• (A B AB)
• Na Cl NaCl
• Decomposition
• (AB A B
• 2H2O2 2H2O O2

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Types of Chemical Reactions

• Single Replacement
• (AB C AC B)
• Mg HCl MgCl2
  H2
• (How do I balance this?)
• Double Replacement
• (AB CD AD BC)
• Na2CO3 CaCl2 NaCl
  CaCO3
• (How do I balance this?)

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