Chemical Reactions

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Chapter 2.4

• Chemical Reactions

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Chemical Changes

• Chemical property the ability of a substance to
  undergo a specific chemical change
• Example Iron combines with Oxygen to form rust
• Ability to rust is a chemical property of iron
• 4Fe 3O2 ? Fe2O3 (rust)

Sulfuric acid and Sugar
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Chemical Changes

• During a chemical change, the composition of
  matter always changesthis is also called a
  chemical reaction
• A substance is changed into NEW substance with
  NEW properties
• Reactant substance present at start
  of the reaction.
• Product substance produced in
  the reaction.

4
What are Chemical Equations?
Chemical Formula shows the ratio of elements in
the compound using chemical symbols H2O shows
2 Hydrogen and 1 Oxygen atoms
Chemical Equation use chemical formulas and
other symbols to summarize a reaction
2 Fe2O3 3 C ? 4 Fe 3 CO2
Reactants Yields
Products
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Chemical Reactions (Rxn)

• Practice write out the reactant(s) product(s)
• 4Fe 3O2 ? Fe2O3
• Reactant(s) _____________
• Product(s) _______________
• Arrow indicates chemical change

4Fe 3O2
Fe2O3
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Recognizing Chemical Changes

• Possible clues include
• heat production
• a change in color
• the production of gas
• the production of a precipitate (a solid that
  forms and settles out of a liquid mixture)
• Every chemical change involves a transfer of
  energy
• Samples must be tested before and after the
  change

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Conservation of Mass

• During any chemical reaction, the mass of the
  products is always equal to the mass of the
  reactants.
• Mass is also constant during physical changes.

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Law of Conservation of Mass

• In any physical change or chemical reaction, mass
  is conserved.
• Mass is neither created or destroyed!!!!
• If mass of product is less than the sum of
  reactantsoften the missing mass escaped in the
  form of gas, or vapor