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Chemistry – Dr. May Notes
Matter
Classification of Matter
Heterogeneous Matter
A mixture is matter that contains two or more different materials.
A physically separate part of a material is called a phase. A phase is a region with
a uniform set of properties.
A heterogeneous mixture is composed of more than one phase. A solid
heterogeneous mixture could be illustrated by a mixture of salt and pepper or sawdust and
gravel. A liquid heterogeneous mixture may be visualized as oil and water.
Homogeneous Matter
Materials that contain only one phase are called homogeneous.
A solution is a homogeneous mixture and is composed of a solute (material
dissolved) and solvent (the material that is doing the dissolving).
Other homogeneous mixtures may be milk (homogenized), cake mix (flour, salt,
sugar), emulsions (soap and oil in water), and a bar of soap (soap, emulsifiers, perfume).
Substances
A substance is a pure homogeneous material that always has the same
composition (pure salt, sugar, sulfur, etc.).
Elements are substances composed of only one kind of atom. These can be found
on the periodic table.
Substances composed of more that one kind of atom are called compounds.
These are chemically bonded together with an ionic or a covalent bond (later discussion).
Organic substances contain the element carbon and inorganic substances usually
do not. An exception to this is the polyatomic ion carbonate, which forms inorganic ionic
compounds like CaCO3, which is calcium carbonate or chalk. Organic compounds
usually have carbon, hydrogen, oxygen (sometimes), and nitrogen (sometimes). The
amino acid glycine is an example. H2NCH2COOH
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Changes in Properties
Physical and Chemical Changes
If the same material remains after a change, it was a physical change. An
example is melting ice to form water. Both ice and water are H2O.
If a different material remains, it was chemical change. An example is burning
hydrogen in oxygen to form water.
2 H2 + O2  2 H2O
The hydrogen and oxygen are both changed to a different material, water. Two elements
are combined to form (synthesize) a compound.
Physical and Chemical Properties
Extensive properties depend on the amount of material present. These include mass,
length, and volume.
Intensive properties do not depend on the amount of matter and are used to identify the
material. These include density, malleability, ductility, and conductivity
Energy
Energy and Chemical Change
Endothermic and exothermic reactions.
Endothermic means that energy is needed to make the reaction happen. An
example of this is the oxidation of copper to form copper oxide.
Exothermic means that the reaction gives off energy. An example of this is the
reaction of magnesium with hydrochloric acid.
Measuring Energy Changes
A calorimeter is used to measure energy changes.
Specific heat – energy needed to raise the temperature of 1 gram of material 1
degree Celsius. For water this is 1.0 calorie or 4.184 joules.
The specific heat (Cp) of water is 4.184 J/gCo
For aluminum:
Cp = 0.902 J/gCo
q =
(m)(T)(Cp)
Heat gained or lost by water (q) (joules) = Mass (m) x change in temperature (T) x
specific heat (Cp) (sometimes designated c).
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