1. Chemical
Reactions
Chapter 19

2. 19-1 How Matter Reacts
Objectives:
Explain what a chemical reaction is.
Distinguish between exothermic and endothermic reactions
Explain chemical equations

3. How Matter Works
• In a chemical reaction, the initial substances are called the
reactants: the new substances produced are called the
products.

4. How Matter Reacts
• Exothermic reactions
• React → Products +
Energy (heat)
• Chemical reactions that
give off energy
• Endothermic Reaction
• Reactants + Energy
(heat) → Products
• Chemical reactions that
need energy

5. How Matter Works
• It is impossible to actually see what goes on in chemical
reactions. It is possible, however, to tell whether or nt a
reaction has taken place.
• Changes in appearance, temperature, and odor all indicate
that a chemical reaction has occurred.
• Scientists describe what happens in a reaction by using
chemical equations that represent with symbols and
formulas the reactants and products in a reaction.

6. 19-2 Types of Chemical
Reactions
• Objectives
• Identify the basic types of reactions
• Explain how types of reactions differ from one another

7. Types of Chemical
Reactions
• Five different kinds of chemical reactions:
• Composition
• Decomposition
• Replacement
• Ionic
• Combustion

8. Chemical Reactions
• Composition reactions occur when two or more atoms
combine
• Composition reaction pattern: A+B→ AB
• Examples: exploding fireworks, a burning
match, catalytic converters in automobiles

9. Decomposition Reactions
• Decomposition reactions occur when a compound breaks
down into simpler substances
• Decomposition reaction pattern: AB→A+B
• Examples: production of lime from limestone, digestion
of food, carbonic acid

10. Combustion Reactions
• Combustion reactions occur when substances are
combined with oxygen, releasing large amounts or light
and heat energy
• Usually involve the burning of hydrocarbons, compounds
made up of carbon and hydrogen
• Examples: burning of natural gas, oil, coal; burning of
wood

11. Replacement Reactions
• Replacement reactions occur when one element is
replaced by a similar element
• Replacement reaction patterns: A +BC → AC + B,
AB + CD → AC + BD.
Examples: copper plating, silver plating, chrome plating

12. Ionic Reactions
• Ionic reactions are similar to replacement reactions
except ions are involved.
• Form precipitates, solids that settle out of the solution.
• Ionic reaction pattern: A+B + C+D →AD + CB
• Examples: pigments used in paints

13. 19-3 Factors That Affect Reactions
• Objective
• Identify and analyze factors that influence the speed of
reactions

14. Factors
• Surface area
• Amount of material
• Temperature
• Catalysts

15. Surface Area
• The more surface area of the reactants that is exposed, the
more atoms can be involved in the reaction, and the faster
the reaction happens.

16. Amount of Material
• The amount of reactants can sometimes affect how
quickly the reaction occurs. Usually, if the amount of
reactants is increased, the speed of the reaction will also
increase.

17. Temperature
• Increasing the temperature speeds up most chemical
reactions because the atoms or molecules move faster.
• Decreasing the temperature slows them down.

18. Catalysts
• Catalysts are substances that speed up the rate of
chemical reactions but are not permanently altered in the
reaction.
• Catalysts do not appear in the final products of the
reactions they affect.

19. Enzymes
• Enzymes are catalysts in your body. They bring about or
speed up chemical reactions.
• Examples:
• salivary gland breaks down starch
• Gastric glands breaks down proteins
• Pancreas breaks down starch
• Intestine breaks down cane sugar, milk sugar

20. 19-4 Acids and Bases
• Objectives
• Describe the characteristics of acids
• Describe the characteristics of bases
• Explain pH

21. Acids and Bases
• The word acid comes from Latin and means “ sour.”
• Scientists describe acids as substances that produce
hydronium ions when they react with water.
• Bases are used to make soap, detergent, and drain cleaner
• A base is substance that releases hydroxide ions, which
give bases their special chemical characteristics.

22. Properties of acids and
bases
Acids
• Formulas begin with H.
• Sour taste
• Turn litmus paper red
• Release hydrogen gas
when they react with
metals
• Examples:
hydrochloric, sulfuric, ace
tic, citric
Bases
• Formulas end with OH
• Bitter taste
• Turn litmus paper blue
• Slippery feel
• Examples:
• sodium hydroxide,
• calcium
hydroxide, magnesium
hydroxide, aluminum
hydroxide

24. Acids and Bases
• You can test for the presence of acids and bases by using special
substances called indicators.
• The strength or weakness of an acid or a base is measured on the pH
scale.
• The pH scale measure how many hydronium ions are in the solution.
• Acids have pH values less than 7, while bases have values greater
than 7.
• A measure of 7 on the pH scale indicates a neutral solution of pure
water, meaning its neither acid or base.
• Neutralization occurs when acids and bases are mixed together.
• The acid and base react chemically to form natural salt and water.