Chemical Reactions by 9uJXRvyL


									Chemical Reactions

     Section 2.4

     Chemical Reactions
 Iron is abundant, easy to shape when
  heated, and relatively strong, especially
  when mixed with carbon in steel. Over
  time, objects made of iron will rust if they
  are left exposed to air. Rusting is a
  chemical change. You will learn to
  recognize chemical changes and to
  distinguish them from physical changes in
  this section.
Chemical Properties and Chemical
 The ability of a substance to undergo a specific chemical
  change is called a chemical property.
 Chemical properties can be used to identify a substance. But
  chemical properties can be observed only when a substance
  undergoes a chemical change.
 Chemical Change- the composition or identity of the
  matter changes. A new substance or new substances are
   This is different from a physical change because during a
    physical change the composition of the matter remains the
Physical Change
 A magnet separates iron from sulfur. This is an example of a
  physical change

Chemical Changes
 A mixture of iron and sulfur is heated. The iron and sulfur
  react and form iron sulfide. This is an example of a
  chemical change.
 Chemical Changes
 A chemical change is also called a chemical reaction.
 One or more substances change into one or more
  new substances during a chemical reaction.
 A substance present at the start of the reaction is a
 A substance produced in the reaction is a product.
 Reactant  Product
       Chemical Changes
 Possible clues to chemical change include:
   a transfer of energy
   the production of a gas
   a change in color
   the formation of a precipitate:

          A precipitate is a solid that forms and settles out of a liquid
Do these 4 indication of chemical change
ALWAYS mean chemical changes??
    Transfer of energy-
      Fire always means chemical change
      Heat, cooling, and light can indicate either type of change. To be
       certain of the type of change, the identity of the substance must
       be examined.
    Production of a gas-
      A gas produced when heat is added, such as during boiling is
       likely to be a physical change
      The production of gas without the addition of heat indicates a
       chemical change
Do these 4 indication of chemical change
ALWAYS mean chemical changes??
    Change in color
      If blue and yellow are mixed and form green, this is likely a
       physical change.
      If 2 clear solutions are combined and a colored solution forms,
       this is a chemical change.
        In other words, if an unexpected color change occurs, a chemical change
    Precipitate
      If dirt settles out of a mixture of dirty water, this is not a true
       precipitate- this is a physical change.
      A true precipitate- one that forms from 2 solutions- always
       indicates a chemical change.
Conservation of Mass
   The law of conservation of mass states that in
    any physical change or chemical reaction, mass is
   The conservation of mass is easily observed when a
    change occurs in a closed container.

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