1. Chapter 9 Chemical Reactions
Mr. Stripling
Pre-AP Chemistry

2. Chemical Reactions
Page 282
The process by which atoms of one or more substances are rearranged to form different substances (a.k.a. chemical change)
Chemical reactions in everyday life:
Breakdown of food in digestion, providing energy to live
In the engines of vehicles
Producing natural fibers (cotton and wool) in plants and animals

3. Evidence of a Chemical Reaction
Temperature change
Release of energy in the form of heat and light
Absorption of heat
Color change
Iron rusting (e.g. turning from a silver to an orange-brown)
Banana changing from green to yellow
Changes in odor, gas bubble and solid formations

4. Representing Chemical Reactions
Equations are used to represent chemical reactions
Equations show reactants and products
Reactants – the starting substances
Products – the substances formed during the reaction
Chemical equations show the direction in which the reaction progresses
An arrow is used to separate the reactants from the products, not an equal sign
Reactants are written to the left of the arrow and products to the right
Read the arrow as react to produce or yield

5. When there are two or more products or two or more reactants a plus sign is used to separate the products from one another and the reactants from one another
Symbol
Purpose +
Separates two or more reactants or products 
Separates reactants from products 
Separates reactants from products and indicates a reversible reaction
(s)
Identifies a solid state
(l)
Identifies a liquid state
(g)
Identifies a gaseous state
(aq)
Identifies a water solution

6. Word Equations Aluminum(s) + bromine(l)  aluminum bromide(s)
Aluminum and bromine react to produce aluminum bromide

7. Skeleton Equations
Uses chemical formulas to identify the reactants and the products
Aluminum and bromine react to yield aluminum bromide
Al(s) + Br2(l)  AlBr3(s)
Carbon and sulfur react to produce carbon disulfide
C(s) + S(s)  CS2(l)

8. Practice Problems
Page 284
Problems 1, 2, and 3

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

10. Balancing Chemical Equations
To balance an equation, you must find the correct coefficients for the chemical formulas in the skeleton equation.
A coefficient in a chemical equation is the number written in front of a reactant or product
Usually whole numbers
Usually not written if the value is one

11. Steps for Balancing Equations
Process
Example 1
Write the skeleton equation for the reaction
H2(g) + Cl2(g)  HCl(g) 2
Count the atoms of the elements in the reactants
H Cl2
2 H atoms Cl atoms 3
Count the atoms of the elements in the products
HCl
1 H atom + 1 Cl atom 4
Change the coefficients to make the number of atoms of each element equal on both sides of the equation (balance the equation)
H2(g) + Cl2(g)  2HCl(g) 5
Write the coefficients in their lowest possible ratio
1:1:2 6
Check your work
2 H atoms + 2 Cl atoms  2 H and Cl atoms

12. Practice Problems
Page 287
Problems 4, 5, and 6

13. Obeying the Law of Conservation of Mass
All chemical reactions obey the law that matter is neither created nor destroyed
Chemical reactions must include sufficient information to show that the reaction obeys the law of conservation of mass

14. Review
The process by which atoms of one or more substances are rearranged to form different substances is called what?
What can act as evidence that a chemical change has occurred?
What is used to separate the reactions from the products in an equation?

15. Chemical Reaction Balancing Game
equations/latest/balancing-chemical-equations_en.html

16. Types of Chemical Reactions
Page 289
Synthesis
Combustion
Decomposition
Replacement
Some reactions have multiple types

17. Synthesis Reactions
A chemical reaction in which two or more substances (A and B) react to produce a single product (AB)
A + B  AB
Sodium and chlorine react to produce sodium chloride
Na + Cl  NaCl

18. Synthesis reactions can also occur between a compound and an element
Two compounds can also be combined to form a compound in a synthesis reaction
Calcium oxide (CaO) and water (H20)
CaO(s) + H20(l)  Ca(OH)2(s)
Synthesis reactions can also occur between a compound and an element
Sulfur dioxide (SO2) reacts with oxygen (O2) to for sulfur trioxide (SO3)
2SO2(g) + O2(g)  2SO3(g)

19. Combustion Reactions
Oxygen combines with a substance and releases energy in the forms of heat and light
The reaction between hydrogen and oxygen produces a combustion reaction
2H2(g) + O2(g)  2H20(g)
When coal (composed mostly of carbon) is burned in the presence of oxygen
C(s) + O2(g)  CO2(g)
Both of these combustion reactions also act as synthesis reactions

20. Not all combustion reactions will also react as synthesis reactions
The combustion reaction involving methane gas (CH4) and oxygen has one substance replace another
CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)

21. Practice Problems
Page 291
Problems 14, 15, 16, and 17

22. Decomposition Reactions
A single compound breaks down into two or more elements or new compounds
The opposite of a synthesis reaction
AB  A + B
Often require an energy source (heat, light, electricity)
Ammonium nitrate breaks down into dinitrogen monoxide and water when the reactant is heated
NH4NO3(s)  N2O(g) + 2H2O (g)

23. Practice Problems
Page 292
Problems 18 and 19

24. Replacement Reactions
Involve the replacement of an element in a compound
Also called displacement reactions
Two types of replacement reactions
Single-replacement reactions
Double-replacement reactions

25. Single-Replacement Reactions
A reaction in which the atoms of one element replace the atoms of another element in a compound
A + BX  AX + B
Lithium atom replacing one of the hydrogen atoms in a water molecule
2Li(s) + 2H2O(l)  2LiOH(aq) + H2(g)
When copper is placed in aqueous silver nitrate
Cu(s) + 2AgNO3(aq)  2Ag(s) + Cu(NO3)2(aq)

26. Note: metals won’t always replace other metals in a compound dissolved in water because metals differ in their reactivities
Reactivity – the ability to react with another substance
Single-replacement reactions are used to determine the placement of metals on the list

27. The reactivity series can be used to predict if a reaction will occur
A metal can replace any metal listed below it that is in a compound
It cannot replace any metal listed above it
Copper atoms replaced silver atoms in a solution of silver nitrate in the previous single-replacement reaction example
Silver in aqueous copper(II) nitrate, the silver will not replace the copper
Ag(s) + Cu(NO3)2(aq)  NR
NR (no reaction)
Silver is listed below copper in the series, resulting in no reaction

28. Nonmetals can also replace nonmetals in single- replacement reactions
Halogens are typically involved
Like metals, halogens have different activity levels
A more reactive halogen will replace a less reactive one
Fluorine replaces bromine in water containing dissolved sodium bromide
F2(g) + 2NaBr(aq)  2NaF(aq) + Br2(l)
Bromine will not replace fluorine in water containing dissolved sodium fluoride
Br2(g) + 2NaF(aq)  NR

29. Practice Problems
Page 295
Problems 21,22, 23, and 24

30. Double-Replacement Reactions
Involves an exchange of ions between two compounds
AX + BY  AY + BX
A and B represent cations and X and Y represent anions
The reaction between calcium hydroxide and hydrochloric acid is a double-replacement reaction
Ca(OH)2(aq) + 2HCl(aq)  CaCl2(aq) + 2H2O(l)
Water is one of the products
When sodium hydroxide and copper(II) chloride react it is a double- replacement
2NaOH(aq) + CuCl2(aq)  2NaCl(aq) + Cu(OH)2(s)
A solid was produced in this chemical reaction; this is called a precipitate

31. Products of Double-Replacement Reactions
All double-replacement reactions produce one of the following
Water, a precipitate, or a gas
Potassium cyanide and hydrobromic acid react to produce a gas
KCN(aq) + HBr(aq)  KBr(aq) + HCN(g)

32. Guidelines for Writing Double-Replacement Reactions
Step
Example
1. Write the components of the reactants in a skeleton equation
Al(NO3)3 + H2SO4
2. Identify the cations and the anions in each compound
Al(NO3)3 has Al3+ and NO3-
H2SO4 has H+ and SO42-
3. Pair up each cation with the anion from the other compound
Al3+ pairs with SO42-
H+ pairs with NO3-
4. Write the formulas for the products using the pairs from Step 3
Al2(SO4)3
HNO3
5. Write the complete equation for the double-replacement reaction
Al(NO3)3 + H2SO4  Al2(SO4)3 + HNO3
6. Balance the equation
2Al(NO3)3 + 3H2SO4  Al2(SO4)3 + 6HNO3

33. Practice Problems
Page 297
Problems 25, 26, and 27

34. Prediction Products of Chemical Reactions
Type of Reaction
Reactants
Probable Products
Generic Equation
Synthesis
Two or more substances
One compound
A + B  AB
Combustion
A metal and oxygen
A nonmetal and oxygen
A compound and oxygen
The oxide of the metal
The oxide of the nonmetal
Two or more oxides
A + O2  AO
Decomposition
Two or more elements and/or compounds
AB  A + B
Single-replacement
A metal and a compound
A nonmetal and a compound
A new compound and the replaced metal
A new compound and the replaced nonmetal
A + BX  AX + B
Double-replacement
Two compounds
Two different compounds produced, one of which will be a solid, water, or a gas
AX + BY  AY + BX

35. Review
Page 298
Problems 29, 30, 31, 32, 33, and 34

36. Aqueous Solutions
Page 299
Contain one or more substances called solutes dissolved in a solvent
Solvent – the most plentiful substance in the solution
Water will always be the solvent in aqueous solutions

37. Ionic Compounds in Solution
When ionic compounds dissolve in water, their ions can separate
This process is called dissociation
An aqueous solution of NaCl contains Na+ and Cl- ions

38. Types of Reactions in Aqueous Solutions
Some reactions in aqueous solutions produce precipitates
2NaOH(aq) + CuCl2(aq)  2NaCl(aq) + Cu(OH)2(s)
The equation does not show every detail, however
Sodium hydroxide and copper(II) chloride are ionic compounds
In aqueous solutions they exist as Na+, OH-, Cu+2, and Cl- ions

39. Ionic Equations
Like chemical equations but show substances that are ions in a solution as ions in the equation
Consider the previous example:
2NaOH(aq) + CuCl2(aq)  2NaCl(aq) + Cu(OH)2(s)
To write it as an ionic equation, write the reactants and products as ions
2Na+(aq) + 2OH-(aq) + Cu+2(aq) + 2Cl-(aq)  2Na+(aq) + 2Cl-(aq) + Cu(OH)2(s)

40. Notice the sodium and chloride ions are both reactants and products?
Complete ionic equation – shows all of the particles in a solution as they exist
Notice the sodium and chloride ions are both reactants and products?
2Na+(aq) + 2OH-(aq) + Cu+2(aq) + 2Cl-(aq)  2Na+(aq) + 2Cl-(aq) + Cu(OH)2(s)
These ions are not participating and are called spectator ions
Spectator ions are typically not shown in Ionic Equations
Net Ionic Equations are ionic equations that include only participating ions in a reaction
2OH-(aq) + Cu+2(aq) +  Cu(OH)2(s)
Only the hydroxide and copper(II) ions are shown in the net ionic equation

41. Practice Problems
Page 302
Problems 35, 37, 38

42. Water Producing Reactions
Chemical Equation:
HBr(aq) + NaOH(aq)  H20(l) + NaBr(aq)
The Complete Ionic Equation:
H+(aq) + Br-(aq) + Na+(aq) + OH-(aq)  H20(l) + Na+(aq) + Br-(aq)
The Net Ionic Equation:
H+(aq) + OH-(aq)  H20(l)

43. Practice Problems
Page 304
Problems 40, 41, and 42

44. Gas Producing Reactions
Chemical Equation:
2HI(aq) + Li2S(aq)  H2S(g) + 2LiI(aq)
The Complete Ionic Equation:
2H+(aq) + 2I-(aq) + 2Li+(aq) + S-2(aq)  H2S(g) + 2Li+(aq) + 2I-(aq)
The Net Ionic Equation:
2H+(aq) + S-2 (aq)  H2S(g)

45. Practice Problems
Page 306
Problems 45-47

46. Overall Equations
When solutions are combined, multiple reactions can occur at once
An equation that combines two reactions is called an overall equation
To write an overall equation, the two reactions are first written
Reaction 1: HCl(aq) + NaHCO3(aq)  H2CO3(aq) + NaCl(aq)
Reaction 2: H2CO3(aq)  H2O(l) + CO2(g)
Then any substances that are on both sides of the equation are cancelled out
Combined Equation: HCl(aq) + NaHCO3(aq)  H2O(l) + CO2(g) + NaCl(aq)
Complete Ionic Equation: H+(aq) + Cl-(aq) + Na+(aq) + HCO3-(aq)  H2O(l) + CO2(g) + Na+(aq) + Cl-(aq)

47. The sodium and chloride ions are acting as spectator ions, so they are left out in the Net Ionic Equation
H+(aq) + HCO3-(aq)  H2O(l) + CO2(g)

48. Review
Page 308
Problems 50, 51, 52, and 55