Download C6-Chemical Reactions

Chemical Reactions
SLO for 2/10/16
Students will be able to distinguish Chemical Properties
and Changes from Physical Properties and Changes.
Homework Check!
12. Mixtures are classified as either heterogeneous or
homogeneous
13. Color, Hardness, Melting Point, Boiling Point, Conductivity,
etc. All are physical properties.
15. a. Homogeneous b. Heterogeneous
c. Homogeneous d. Heterogeneous
17. Filtration is used to separate solids from liquids. Example:
Distillations is used to separate liquids from substances
dissolved in other liquids. Example:
Vocab Review!
 Solid
 Solutions
 Liquid
 Physical Property
 Gas
 Physical Change
 Phase
 Independent Variable
 Constant
 Dependent Variable
 Theory
 Mass
 Scientific Law
 Filtration
 Distillation
 Volume
 Hypothesis
 Substance
 Extensive Property
 Intensive Property
 Mixture
Elements
 An element is the simplest form of matter that has a unique
set of properties.
 Can be an atom or a diatomic molecule
 Molecule- 2 or more atoms bonded together
 Diatomic molecule- molecule containing 2 atoms of the same
element
 There are 7 of them: H2, N2, O2, Cl2, F2, Br2, I2
 Elements can be found on the periodic table
 Elements can’t be broken down physically or chemically
Compounds
 A compound is a substance that contains two or more elements
chemically combined in a fixed proportion
 Can be broken down by chemical means but not by physical means
 Fixed proportion- this means that the ratio of elements is the same
in every particle of the compound
 Water always contains 2 hydrogen atoms for every 1 oxygen atom
 Methane always contains 4 hydrogen atoms for every 1 carbon atom
Breaking Down Compounds
 A chemical change is a change
that produces matter with a
different composition than the
original matter

When table sugar is heated, it goes through a
series of chemical changes. You can see the
change as the sugar is burned.
Distinguishing Elements and
Compounds
 The final products of these chemical changes are solid carbon and water
vapor. The following diagram summarizes the process.

Properties of Compounds and
Elements
 In general, the properties of compounds are
quite different from those of their component
elements.
 Sodium- explosive, soft, lustrous metal
 Chlorine- greenish yellow, poisonous gas
 Sodium Chloride- table salt!
 Chlorine is used to kill harmful
organisms in swimming pools.
Sodium
 Sodium is stored under oil to
keep it from reacting with
oxygen or water vapor in the
air. Sodium vapor produces
the light in some street lamps.
Sodium Chloride
 Sodium Chloride (commonly
known as table salt) is used to
season or preserve food.
Problem Solving- Element or Compound
Chemical Symbols
 We use Chemical Symbols to represent elements and
combinations of chemical symbols to represent compounds
 Previously used chemical symbols:
Current Chemical Symbols
 Elements are represented by chemical symbols:
 Atoms: C, He, B, Be, Ar, Ne
 Diatomic molecules: H2, N2, O2, Cl2, F2, Br2, I2
 Compounds are represented by formulas:
 Formulas are combinations of chemical symbols with numbers
written as subscripts to indicate how many atoms of each
element are present.
 H2O, CH4, C6H12O6, CO, NO
More Chemical Symbols
The Periodic Table
 Period- Horizontal rows on the periodic table
 There are seven periods and the number of elements in each
varies
 Group- Vertical columns on the periodic table
 Elements within a group have similar chemical and physical
properties
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
Changes
 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
formed.
 This is different from a physical change because during a
physical change the composition of the matter remains the
same.
Physical Change
 A magnet separates iron from sulfur. This is an example of a
physical change
2.4
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
reactant.
 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:
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

A precipitate is a solid that forms and settles out of a liquid
mixture.
Do these 4 indications 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 indications 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
occurred.
 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
conserved.
 The conservation of mass is easily observed when a
change occurs in a closed container.
Classwork
 Reading Assignment: Section 2.4
 Written Assignment: pg. 50, #32-34, 36-38