4 Ways a Rxn can be Recognized

1
4 Ways a Rxn can be Recognized

• An unexpected color change.
• Ex) 2 clear solutions producing a yellow color.
• 2. A solid forms.
• 3. A gas forms Ex) Zn HCl ? H2 (g)
• 4. A change in temperature. Heat is absorbed
  (endothermic) or release (exothermic).

2
Characteristics of a Chemical Rxn

• All chemical reactants involve energy usually in
  the form of heat.
• Sometimes energy is needed to get a reaction
  going ex) fireworks
• Sometimes energy is released.
• Some reactions are fast. Ex) explosives.
• Some reactions are slow. Ex) rusting

3
Chemical Compounds

• Compound a substance composed of 2 or more
  elements chemically joined together.
• Characteristics of Compounds
• Compounds can form when different atoms share
  electrons are attracted to each other.
• When this happens, each element loses its own
  properties.
• Ex) Na explosive, Cl poisonous gas NaCl
  table salt

4
Characteristics con.

• C. New compound now has new properties.
• D. The shorthand expression for a compound is a
  formula.
• The shorthand expression for an element is a
  symbol.
• The subscript is the number of atoms of each
  element in a compound.
• The coefficient is the large number in front of
  the formula. It tells how many molecules of the
  substance there are.

5
Synthesis

• A reaction in which two or more elements join
  together to form a compound. (synthesis means to
  put together)
• Ex) A B ? AB (where A and B are elements)
• 4Al 3O2 ? 2Al2O3
• 2 Mg O2 ? 2MgO

6
Decomposition

• A reaction in which a compound is broken down
  into its elements or simpler compounds.
  (decomposition means to break down)
• Ex) AB ? A B (where AB is a compound)

7
Single and Double Replacement

• Single Replacement a reaction in which elements
  break away from one substance and join with a NEW
  partner.
• Ex) A BC ? B AC
• Double Replacement a reaction in which 2
  compounds switch partners (elements)
• Ex) AB CD ? AD CB (Wife Swap)

8
Reduction oxidation (Redox)

• A reaction that occurs when electrons are
  transferred from one reactant to another.
• Ex) iron metal reacting with oxygen Fe2O3
• Substances that lose electrons are oxidized. OIL
• Substances that gain electrons are reduced. RIG
• Combustion combine with oxygen to produce CO2
  and H2O
• Ex) CH4 2O2 ? CO2 2H2O

9
Chemical Equations

• Scientists write chemical reactions in a
  short-hand form. This is called an equation.
• Parts of an Equation
• The arrow is called yields
• Chemicals are represented by their symbols or
  formulas.
• Subscripts are numbers below the line.
• Coefficients are the big number in front of the
  symbol or formula.

10
Parts of an Equation con.

• 5. Reactants are the substances left of the
  arrow.
• 6. Products are the substances to the right of
  the arrow.
• 7. System is the entire equation.
• 8. Balancing the Equation the same number and
  kinds of atoms must be present in the reactant
  and in the products. To balance you use
  COEFFICIENTS.