Transcript Physical and Chemical Changes

Physical and
Chemical Changes
Intro to Chemistry
Physical Properties
Physical Property: Any characteristic of a
material that can be observed or measured
without changing the composition (make up) of
the substances in the material.
Seven examples of Physical Properties
• Viscosity
• Conductivity
• Malleability
• Hardness
Melting Point
Boiling Point
Density
Physical Properties
 Viscosity: The tendency of a liquid to keep
from flowing (syrup has MORE viscosity than
water).
 Conductivity: A material’s ability to allow
heat to flow.
 Malleability: The ability of a solid to be
hammered without shattering.
Physical Properties
 Hardness: Compare hardness of objects by
seeing which one would scratch the other.
 Melting Point: The temp. at which a
substance changes from solid to liquid.
 Boiling Point: The temp. at which a
substance changes from liquid to gas.
 Density: can be used to test the purity of a
substance.
Physical Changes
Physical Change: Occurs when some of the
properties of a material change, but the
composition of the substance stays the same.
 Any change in the form or appearance of
matter.
 A physical change DOES NOT change the
substances chemical makeup.
 A physical change DOES NOT produce a new
substance.
Physical Changes
 There are TWO types of physical changes.
• Reversible Change: A change that can be
changed back to its original form.
• Irreversible Change: A change that CANNOT be
changed back to its original form.
Examples of Physical Changes
Reversible
Hair being put into a pony tail
Iron removing wrinkles
Examples of Physical Changes
Reversible
Crumpling Paper
Solid to Liquid to Solid – ANY Phase Change
Examples of Physical Changes
Reversible
Crushing a Can
Folded Shirt
Examples of Physical Changes
Irreversible
Cutting a Piece of Paper
Sliced Tomato
Peeled Orange
Hair Cut
Chemical Change
Chemical Change: When one substance reacts and
forms one or more new substances.
A chemical reaction occurs when atoms are rearranged
not taken away or added.
For you to know that a chemical change has happened
A NEW SUBSTANCE MUST BE PRODUCED!!!!
Evidence of a chemical change:
 Oxidation (rusting)
Flammability
 Production of Gas (Bubbles)
Warming or Cooling
 Formation of a Precipitate (Two Liquids form a solid)
Physical Changes & Mixtures
** Reminder: A physical change DOES
NOT produce a new substance**
Two Main Types of Mixtures
Heterogeneous Mixture
Homogeneous Mixture
Physical Changes & Mixtures
Heterogeneous Mixture: A mixture in which substances
are NOT evenly mixed.
In a heterogeneous mixture…
 You can easily see the different parts of the mixture
OR
 You can only see the different parts of a mixture with
a microscope.
Physical Changes & Mixtures
Example – Blood looks evenly mixed; its color and
texture are the same throughout.
Under a microscope you can
see the uneven mixing.
Physical Changes & Mixtures
Example – Granite or Fruit Salad. You can easily see the
different parts that make up the substance.
Physical Changes & Mixtures
Homogeneous Mixture: A mixture in which substances
are evenly mixed.
In a homogeneous mixture…
 You CANNOT easily see the different parts of the
mixture
Chemical Reactions
Chemical changes either absorb or release heat!
These reactions are called Endothermic and Exothermic
Reactions.
When you need to determine if a reaction is
endothermic or exothermic, watch how the temperature of
the surroundings changes.
 Endothermic reaction – chemical reactions that absorb
thermal energy (heat). Cools the surroundings.
 Exothermic reaction – chemical reaction that releases
thermal energy (heat). Heats the surroundings.
Endothermic & Exothermic
Reactions
Label each example as Endothermic or Exothermic.
Melting Ice Cubes
A Candle Flame
Cooking an Egg
Making Ice Cubes
Condensation of Water from Water Vapor
Evaporation of Water