CHEMICAL REACTIONS

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CHEMICAL REACTIONS
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CHEMICAL REACTIONS

• By
• JAMES G. GOGOLOS

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OBJECTIVES

• Describe the characteristics of chemical
  reactions.
• Compare endothermic and exothermic reactions.
• Describe how chemical reactions are written and
  balanced.
• Identify the four types of chemical reactions.

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OBJECTIVES (continued)

• Compare the properties of acids and bases.
• Describe a neutralization reaction.
• Relate the pH scale to the strengths of acids and
  bases.

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ALMOST EVERYTHING YOU SEE AND USE EACH DAY
INVOLVES A CHEMICAL CHANGE
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CHEMICAL CHANGES

• The changing colors of autumn leaves

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Step 1     iron     oxygen  --gt iron oxide

Step 2   iron oxide    water  --gt   RUST

• Rusting is a chemical process in which iron
  combines with oxygen to form iron oxide.

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• The baking of bread
• The formation of synthetic fibers for clothing

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What is a CHEMICAL REACTION ?
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The process in which the chemical properties of
the original substances disappear as new
substances with different chemical properties are
formed.
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ENERGY CHANGES

• When chemical reactions occur, there is always a
  change in energy.

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EXOTHERMIC REACTIONS

• A CHEMICAL REACTION THAT RELEASES ENERGY

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ENDOTHERMIC REACTIONS

• A CHEMICAL REACTION THAT ABSORBS ENERGY

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REMEMBER

• Whether a chemical reaction is endothermic or
  exothermic, there is always an energy change
  involved.

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LETS REVIEW
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SECTION REVIEW

• 1.What happens to the original substances
  during a chemical reaction ?
• 2.In what type of chemical reaction is energy
  released ? Absorbed ?

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CHEMICAL EQUATIONS
MgO energy
Mg 02

• The statement that uses symbols and formulas to
  describe a chemical reaction

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MgO 02
MgO

• REACTANTS YIELD PRODUCTS

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A Chemical Equation must be BALANCED.

• The number of atoms of each element must be the
  same on both sides of the equation.

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Balancing Chemical Equations

• H2 02

H2O

• Write a chemical equation with correct symbols
  and formulas.
• Count the number of atoms of each element on each
  side of the arrow.
• Balance atoms using COEFFICIENTS only. Never
  change a subscript or a chemical formula.
• Check your work by counting atoms of each
  element.

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COEFFICIENTS

• Numbers that indicate how many atoms of each
  substance are involved in a chemical reaction.

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REMEMBER

• To balance a chemical equation, you can change
  coefficients only.
• NEVER change a subscript or a chemical formula.

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LETS REVIEW
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SECTION REVIEW

• What is a chemical equation ?
• 2. How are chemical equation balanced ?
• 3. What is a coefficient ?

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TYPES OF REACTIONS

• Chemists have identified four
• general types of chemical
• reactions.
• SYNTHESIS
• DECOMPOSITION
• SINGLE REPLACEMENT
• DOUBLE REPACEMENT

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SYNTHESIS REACTIONS

• A B AB

When two or more substances combine to form a new
substance.
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DECOMPOSITION REACTION

• AB A B

When one complex substance breaks down into two
or more simpler substances.
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SINGLE REPLACEMENT

• AB C AC B
• When one element replaces another element in a
  compound.

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DOUBLE REPLACEMENT

• AB CD AC BD
• When two compounds react to form two new
  compounds.

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A fire is a dramatic example of a synthesis
reaction. Burning involves the chemical
combination of a fuel with oxygen. Heat and
light are always produced.
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Carbonic acid is added to liquids to give them
fizz.Carbonic acid, however, quickly
decomposes into carbon dioxide and water.
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LETS REVIEW
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SECTION REVIEW

• Name the four types of chemical reactions.
• What is the difference between a synthesis
  reaction and a decomposition reaction ?
• What is a single-replacement reaction ? A double
  replacement reaction ?

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ACIDS AND BASES
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ACIDS

• Found in fruits, milk, buttermilk, tea,
  pickles, vinegar, and carbonated beverages.

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ACIDS

• Make up a class of compounds that
• 1. Taste sour
• 2. React with certain indicators
• 3. Produce positive hydrogen ions
• when dissolved in water

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INDICATORS

• Compounds that show a definite color change
  when they are mixed with an acid or a base.
• 1. Phenolphthalein
• 2. Litmus Paper

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LITMUS PAPER
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Litmus paper changes from blue to red in the
presence of an acid.
Color change from blue to red
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PHENOLPHTHALEIN

• This liquid stays colorless in the presence of
  acids

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Common ACIDS

• Chemical Name Formula
• hydrochloric HCl
• sulfuric H2SO4
• carbonic H2CO3
• citric H3C6H5O7
• phosphoric H3PO4

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BASES

• Found in household products such as lye, ammonia,
  milk of magnesia, and soaps

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BASES

• 1. Taste bitter
• 2. React with certain indicators
• 3. Produce negative hydroxide ions when dissolved
  in water
• 4. Slippery to the touch

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INDICATORS

• Litmus paper turns from red to blue in bases.

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INDICATORS

• PHENOLPHTHALEIN turns from clear to BRIGHT PINK
  in the presence of bases

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ACID and BASE STRENGTH

• Can be measured by using the pH SCALE

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The pH scale is a series of numbers from 0 to 14.

• Acids - below 7 Bases - above 7
• Neutral
• Substances 7

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pH SCALE
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NEUTRALIZATION

• Acid Base Salt Water

A reaction that produces a salt from the
combination of an acid and a base.
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neutralization
HCl NaOH H2O NaCl
ACID BASE yields WATER SALT