Introduction to Chemical Reactions

1
Introduction to Chemical Reactions

• Making new substances

2
Targets

• I can
• Represent a chemical reaction by writing a
  Chemical Equations.
• Balance Chemical Equations to show the same
  number of atoms of each element on each side.
• Explain that a balanced chemical equation obeys
  The Law of Conservation of Mass (saying that
  atoms wont be created or destroyed in a chemical
  reaction.)
• Analyze a chemical equation. Identify the 5 basic
  types of chemical reactions, reactants, products
• Identify signs of a chemical reaction from lab
  observations

3
How do you know when a chemical reaction takes
place?

• Color Change

• Precipitate Formation

4
How do you know when a chemical reaction takes
place?

• Gas Formation

• Odor

5
How do you know when a chemical reaction takes
place?

• Temperature Change (energy change)

• exothermic

endothermic
6
How do you know when a chemical reaction takes
place?

• Produce light (energy change)

• Change in Acidity

7
Representing Chemical Reactions

• Chemists observe chemical reactions and have come
  up with a shorthand way to represent or model
  what is happening.
• Word equations are written as chemical equations
  by replacing chemical names with correct chemical
  formulas
• Solid Sodium combines with Chlorine gas to make
  solid Sodium Chloride
• 2Na (s) Cl2 (g) ? 2NaCl

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Chemical Equations

• Chemical Equation 2Na Cl2 ? 2NaCl
• Reactants starting substances in chemical
  reaction, written on left side of arrow
• Products substance(s) formed from the reaction,
  written on right side of arrow
• Reactant ? Product
• When more than one reactant or product they are
  separated with a plus () sign
• The arrow ? shows the direction of the reaction

9
Symbols used in Chemical Equations
Symbol Purpose
Separates more than one reactant or product
? Separates reactants from products. Indicates direction of reaction
(s) Identifies a solid state
(aq) Identifies that something is dissolved in water
(l) Identifies liquid state
(g) Identifies gaseous state
10
Law of Conservation of Mass

• In a chemical reaction, matter is neither created
  nor destroyed.
• Atoms wont change their identity (e.g. a Carbon
  atom cant become an Iron atom)
• This means that you have to have the same number
  of each type of atom on each side of the chemical
  equation.
• Conservation of Mass Video

11
Balancing Equations

• After you write a chemical equation you have to
  balance it to make sure that the same number of
  atoms of each element are on each side. (law of
  conservation of mass)

12
Steps to Balancing a Chemical Equation
13
Types of chemical reactions
14
Types of chemical reactions

• Combination two or more substances combine to
  form one product
• Decomposition one substance breaks down into
  two or more simpler substances
• Single replacement one single element replaces
  another
• Double replacement two compounds switch
  cations. Products can be insoluble in
  water(precipitate)
• Combustion - substance (hydrocarbon) combines
  with oxygen to produce carbon dioxide and water
  and energy (exothermic)