1. Chapter 9
Chemical Reactions

2. Section 1
Reactions & Equations

3. Chemical Reaction
The process by which the atoms of one or more substances are rearranged to form different substances.

4. How Can You Tell If A Chemical Reaction Has Taken Place?
Temperature change
Color change
Odor
Gas formation (Bubbles)
Formation of a solid

5. Representing Chemical Reactions
Chemists use statements called equations to represent chemical reactions.
These equations have two parts
Reactants – The starting materials
Products – The substances that are formed during a chemical reaction.

6. Word Equations
Example

7. Skeleton Equation
Example

8. Chemical Equations
A statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction.

9. Balancing Chemical Equations
Recall that matter is neither created nor destroyed in a chemical reaction.
In order to follow the law of conservation of matter we must balance our chemical equations so that the reactant and product sides are equal to one another.

10. Coefficient – In a chemical equation is the number written in front of a reactant or product.
Example
Coefficients are usually whole numbers; the number 1 is usually omitted.

11. Steps for Balancing Equations
Write the skeleton for the reaction.
Count the atoms of the elements in the reactants.
Count the atoms of the elements in the product.
Change the coefficients to make the number of atoms of each element equal on both sides.
Write the coefficients in their lowest possible ratios.
Check your work!

12. Example: Balancing Chemical Equations

13. Classifying Chemical Reactions
Section 2
Classifying Chemical Reactions

14. Types of Chemical Reactions
We will look at five types of chemical reactions.
Each type of reaction will have a general formula that will be helpful in recognizing the type of reaction present.

15. Synthesis Reaction
A chemical reaction in which two or more substances (A and B) react to produce a single product (AB).
General Form
Example

16. Combustion Reaction
In a combustion reaction oxygen combines with a substance and releases energy in the form of heat and light.
In a combustion reaction
𝑂 2 is always present
Usual products are 𝐶𝑂 2 & 𝐻 2 𝑂

17. Decomposition Reaction
A reaction in which a single compound breaks down into two or more elements or new compounds.
General Form
Example

18. Single-Replacement Reaction
A reaction in which the atoms of one element replace the atoms of another element in a compound.
General Form
Example

19. Double-Replacement Reaction
A reaction in which ions between two compounds are exchanged.
General Form
Example

20. Helpful Hints… Nonmetals replace nonmetals
Metals will replace Hydrogen or another metal.
More active metals will replace less active metals (see Figure 13 p.293).
A less active metal will not replace a more active metal.

21. Looking At Double-Replacement Reactions
Only occurs if one of the products is a solid precipitate.
Precipitate – an ionic compound formed by a double-replacement reaction
Which is not soluble in water
It forms a cloudy appearance in the solution; if allowed to sit, the precipitate will settle to the bottom of the container

22. Solubility Rules for Ionic Compounds
Always Soluble (aqueous)
Name
Symbol
Group I Metals
Li+1 Na+1 K+1
Ammonium
NH4+1
Acetate
C2H3O2-1
Nitrate
NO3-1

23. Generally Insoluble (form precipitates)
Name
Symbol
Exceptions
carbonate
CO3-2
Group I Metals, ammonium
chromate
CrO4-2
phosphate
PO4-3
sulfide
S-2
Group I & II Metals, ammonium
hydroxide
OH-1
Group I Metals, Ca+2, Sr+2, Ba+2, ammonium

24. Precipitates with (solid)
Mostly Soluble (usually aqueous)
Name
Symbol
Precipitates with (solid)
halide ions (X)
Cl-1, Br-1, I-1
AgX, HgX2, PbX2
sulfate
SO4-2
SrSO4, BaSO4, PbSO4, Hg2SO4
Use the Solubility Table on p.974

25. Reactions in Aqueous Solutions

26. As we have talked about previously a solution is a homogeneous mixture.
Many of the reactions discussed in the previous section involve substances dissolved in water.
When a substance is dissolved in water, a solution forms.
An aqueous solution contains one or more substances called solutes dissolved in water and water in this case would be the solvent.

27. What Happens In an Aqueous Solution?
Ions form
Example
p.974 Solubility Table

28. Ionic Equations
To show the details of reactants that involve ions in aqueous solutions, chemists use ionic equations.
Ionic equations differ from chemical equations in that substances that are ions in solution are written as ions in the equation.

29. Complete Ionic Equation
An ionic equation that shows all of the particles in a solution as they exist.
Example

30. Spectator Ion
Ions that do not participate in a reaction.
Example

31. Net Ionic Equation
Ionic equations that include only the particles that participate in the reaction.
Spectator ions are not included
Example