Unit 8 Chemical Reactions and Equations

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Unit 8 Chemical Reactions and Equations

• Addison-Wesley Chapter 8

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Brainstorm

• List all the chemical reactions you can think of
  on a piece of paper.
• Try to sort these into groups according to some
  characteristic.

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Chemical Reaction

• What happens in photosynthesis?
• Is this a chemical reaction?
• Definition Process in which one or more
  substances are converted into new substances with
  different physical and chemical properties.
• Name some around you.

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Parts of a Reaction

• Reactants found on the left, this is the
  material that you begin with
• Products found on the right, this is the
  material that is formed
• Look at one equation

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Driving Force

• Why does iron react with oxygen while paper does
  not?
• All reactions involve energy.
• Some are spontaneous (iron)
• Some need a kick (paper)
• Some need constant energy (breaking water down)

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Equations

• Chemical sentence which describes a chemical
  reaction
• Word equation describes everything with words
• Formula equation written using the correct
  formulas for everything
• Practice one

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Symbols

• (s) solid
• (l) liquid
• (g) gas
• (aq) aqueous, dissolved in water
• ? or heat heat (written above the arrow
• A catalyst is written above the arrow
• ? gas is given off
• ? precipitate LEARN THESE!

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Conservation of Matter

• Mass remains constant so the number of atoms of
  each element must be the same on both sides.
• This is called balancing the equation.
• Look at last reaction what is wrong?

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Rules

• Write all the correct formulas
• This is a skeleton equation
• Balance using only coefficients, do not touch the
  formulas!
• PRACTICE

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Diatomic Elements

• These elements are always diatomic when free in
  nature
• H2 N2 O2 F2 Cl2 Br2 I2
• Brinclhof

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Kinds of Reactions

• There are 5 main kinds of reactions
• Combination
• Decomposition
• Single Replacement
• Double Replacement
• Combustion

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Combination

• Also called a synthesis reaction
• Elements or compounds come together to form one
  product.
• One substance on the right is the way to
  recognize this kind of reaction.
• A B ? AB
• Examples

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Decomposition

• What does the word mean?
• In this reaction, there is only one reactant
• The reactant breaks down into elements or
  compounds
• AB ? A B
• Examples
• Usually requires energy

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Single Replacement Reactions

• Also called single displacement
• Like a single cutting in on a couple
• It is one element replacing another element in a
  compound, to form a new compound and a free
  element
• Often metals or halogens

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Activity Series

• One element must cause electron transfer
• Need a list to be able to decide if a reaction
  will occur.
• Handout Activity Series of Metals
• Halogens are in order of reactivity
• (F is most reactive)
• A BC ? AC B

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Double Replacement

• Also called Double Displacement
• Like two couples dancing and switching partners
• This is done in solution
• Usually a precipitate forms
• AB CD ? AD CB

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Combustion

• Combining of a fuel with oxygen to form CO2 and
  H2O
• This is called complete combustion
• Fuel is often a hydrocarbon
• A great deal of energy is released

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Incomplete Combustion

• Occurs when oxygen becomes limited (like in a
  closed garage)
• Products shift to CO and H2O
• Dangerous
• CO stays bonded to hemoglobin and you cannot take
  in oxygen
• This is carbon monoxide poisoning