Claremont High School Physical Science

 All reaction types can be divided into two types of changes: Physical or Chemical

Physical Change:  No new substance is formed  These changes are easily reversible or temporary

 Dissolving salt in water  Melting, boiling  Mixing of two solids or liquids

Chemical Change:  A new substance is formed  These changes are irreversible or permanent  The new substance formed will have different properties

1. The new substance has a different appearance such as color or physical state  Example: Electrolysis of water  Reason: Electrolysis of water produces two new substances – Hydrogen and oxygen gas.  Hydrogen and Oxygen are gases but water is a liquid.

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2. A lot of heat is given out in a chemical change.  Example:

 A chemical reaction is when a substance turns into another substance  Chemical reactions are chemical transformations.  Example: Single displacement reaction. A + CB  AB + C Zn + 2HCl  ZnCl2 +H2

1. What is the difference between a chemical and physical change? 2. What are some examples of a chemical change? List at least 3.

 Physical or chemical change?  The rain turned to snow…  Marty broke a class on the bathroom floor…  I burned my bagel!  I fried eggs for breakfast…  I mixed baking soda and vinegar for science class…  I heated sand to its melting point…

 An element is a pure substance which cannot be split up into two or more simpler substances by physical or chemical means.  Sugar is not an element as it can be broken down into carbon and water.

 An element consists of only one type of atom.  An element can exist as atoms (ex: argon) or molecules (ex: nitrogen)

 Very few elements exists as atoms besides helium and neon.  Most elements exist as molecules.

AtomsMolecules Smallest particle of an element and has the same chemical properties of the element. Made up of two or more atoms that are chemically bonded together.

 A compound is a substance which is made up of two or more elements chemically combined together. Molecules Compounds OR Molecules

 A compound can be broken down into a simpler type of matter (elements)  A compound can be broken down by chemical, but NOT physical means.

 Are the following substances atoms, elements, molecules or compounds?

 A mixture is formed when substances combine in a physical way.  Dissolving, melting, mixing  A mixture can be separated in a physical way.  Dissolving, evaporating, filtering, picking pieces out with your hand

 Heterogeneous mixtures are mixtures that don’t have their parts spread evenly.  Homogeneous mixtures are mixtures where the parts are spread evenly.

 Homogeneous or Heterogeneous?  Sugar  Flat soft drink (no bubbles)  Soil  Paint  Beach sand  Chunky spaghetti sauce  Aluminum foil