1. Introductory Chemistry, Seventh Edition Charles H. Corwin
Chapter 7. Chemical Reactions
Modified by: Dr. Violeta F. Coarfa 1

2. Types of Changes
A physical change does not alter the composition or identity of a substance.
ice melting
sugar dissolving
in water
A chemical change alters the composition or identity of the substance(s) involved.

3. Learning Check Classify each of the following as a
1) physical change or 2) chemical change.
A. ____Burning a candle.
B. ____Ice melting on the street.
C. ____Toasting a marshmallow.
D. ____Cutting a pizza.
E. ____ Melting a candle.

4. Solution Classify each of the following as a
1) physical change or 2) chemical change.
A Burning a candle.
B Ice melting on the street.
C Toasting a marshmallow.
D Cutting a pizza.
E Melting a candle.

5. Chemical Reaction old bonds are broken and new bonds are formed.
In a chemical reaction
a chemical change that produces one or more new substances.
there is a change in the composition of one or more substances.
old bonds are broken and new bonds are formed.
atoms in the reactants are rearranged to form one or more different substances.

6. Evidence for Chemical Reactions
There are four observations that indicate a chemical reaction is taking place.
A gas is released.
Gas may be observed in many ways in a reaction from light fizzing to heavy bubbling.
An insoluble solid is produced.
A substance dissolves in water to give an aqueous solution.
If we add two aqueous solutions together, we may observe the production of a solid substance.
The insoluble solid formed is called a precipitate.
A permanent color change is observed.
A energy change is observed.
A reaction that releases heat is an exothermic reaction.
A reaction the absorbs heat is an endothermic reaction.
Examples of a heat energy change in a chemical reaction are heat and light given off.

7. Learning Check
Which of the following is experimental evidence for a chemical reaction?
a. Pouring vinegar on baking soda gives foamy bubbles.
b. Mixing two solutions produces insoluble particles.
c. Mixing two colorless solutions gives a yellow solution.
d. Mixing two solutions produces a temperature increase.
Solution:
We can analyze each of these observations based on the criteria for a chemical reaction.
a. The bubbles produced indicate a chemical reaction is occurring.
b. The insoluble particles formed indicate a chemical reaction.
c. The yellow color produced indicates a chemical reaction.
d. The temperature increase indicates heat energy is being released from a chemical reaction.
Practice Exercise
What are four observations that a chemical reaction has occurred?

8. Diatomic Molecules
Seven nonmetals occur naturally as diatomic molecules:
Hydrogen (H2)
Nitrogen (N2)
Oxygen (O2)
Halogen (F2)
Halogen (Cl2)
Halogen (Br2)
Halogen (I2)
These elements are written as diatomic molecules when they appear in chemical reactions.

9. Chemical Equations
A chemical equation – symbolic representation of a chemical reaction
the formulas of the reactants on the left of the arrow.
the formulas of the products on the right of the arrow.
Reactants Product

10. Chemical Equation Symbols
Here are several symbols used in chemical equations:

11. Chemical Equations are Balanced
In a balanced
chemical reaction
no atoms are lost or gained.
the number of reacting atoms is equal to the number of product atoms.
Copyright © by Pearson Education, Inc.

12. A Study Tip: Using Coefficients
When balancing a chemical equation,
- use one or more coefficients to balance atoms.
- never change the subscripts of any formula.
N O NO Not Balanced
N O N2O2 Incorrect formula
N O NO Correctly balanced
using coefficients
The coefficients must be whole numbers.
If you get a fraction, multiply the whole
equation by the denominator to get whole
Numbers.
[H2(g) + ½ O2(g) → H2O(l)] x 2
2 H2(g) + O2(g) → 2 H2O(l)
Check that you have the smallest whole
number ratio of coefficients.
[2 H2(g) + 2 Br2(g) → 4 HBr(g)] ÷ 2
H2(g) + Br2(g) → 2 HBr(g)

13. Learning Check State the number of atoms of each element on the
reactant side and the product side for each of the
following balanced equations.
A. P4(s) Br2(l) PBr3(g)
4 P atoms = 4 P atoms
12 Br atoms = Br atoms
B. Al(s) Fe2O3(s) Fe(s) Al2O3(s)
2 Al atoms = 2 Al atoms
2 Fe atoms = Fe atoms
3 O atoms = 3 O atoms

14. Learning Check
Balance each equation and list the coefficients in the balanced equation going from reactants to products:
A. __Mg(s) + __N2(g) __Mg3N2(s)
1) 1, 3, ) 3, 1, ) 3, 1, 1
B. __Al(s) + __Cl2(g) __AlCl3(s)
1) 3, 3, 2 2) 1, 3, ) 2, 3, 2

15. Solution A. 3) 3, 1, 1 3Mg(s) + 1N2(g) 1Mg3N2(s) B. 3) 2, 3, 2
2Al(s) Cl2(g) AlCl3(s)

16. Balancing with Polyatomic Ions
Na3PO4(aq) + MgCl2(aq) Mg3(PO4)2(s) + NaCl(aq)
Balance PO43- as a unit
2Na3PO4(aq) + MgCl2(aq) Mg3(PO4)2(s) + NaCl(aq)
2 PO = PO43-
Check Na + balance
6 Na = Na+
Balance Mg and Cl
2Na3PO4(aq) + 3MgCl2(aq) Mg3(PO4)2(s) + 6NaCl(aq)
3 Mg = 3 Mg2+
6 Cl = Cl-

17. Learning Check
Balance and list the coefficients from reactants to products.
A. __Fe2O3(s) __C(s) __Fe(s) __CO2(g)
1) 2, 3, 2, ) 2, 3, 4, ) 1, 1, 2, 3
B. __Al(s) + __FeO(s) __Fe(s) __Al2O3(s)
1) 2, 3, 3, ) 2, 1, 1, ) 3, 3, 3, 1
C. __Al(s) + __H2SO4(aq) __Al2(SO4)3(aq) + __H2(g)
1) 3, 2, 1, ) 2, 3, 1, ) 2, 3, 2, 3 17

18. Solution A. 2) 2, 3, 4, 3 2Fe2O3(s) + 3C(s) 4Fe(s) + 3CO2(g)
B. 1) 2, 3, 3, 1
2Al(s) + 3FeO(s) Fe(s) + 1Al2O3(s)
C. 2) 2, 3, 1, 3
2Al(s) + 3H2SO4(aq) Al2(SO4)3(aq) + 3H2(g)

19. Type of Reactions Chemical reactions can be classified as
combination reactions.
decomposition reactions.
single replacement reactions.
double replacement reactions.
neutralization reactions

20. Combination In a combination reaction,
two or more elements form one product.
or simple compounds combine to form one product. +
2Mg(s) + O2(g) 2MgO(s)
2Na(s) + Cl2(g) 2NaCl(s)
SO3(g) + H2O(l) H2SO4(aq) A B

21. Decomposition In a decomposition reaction,
one substance splits into two or more simpler substances.
2HgO(s) Hg(l) + O2(g)
2KClO3(s) KCl(s) + 3 O2(g) D
CaCO3  CaO + CO2
Practice Exercise
Write a balanced chemical equation for each of the following decomposition reactions:
a. Barium hydrogen carbonate is decomposed with heat.
b. Copper(I) hydrogen carbonate is decomposed with heat.

22. Single Replacement In a single replacement reaction,
one element takes the place of a different element in another reacting compound.
Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)
Fe(s) + CuSO4(aq) FeSO4(aq) + Cu(s)

23. Types of Single-Replacement Reactions+1 +2
Sr + 2H2O Sr(OH)2 + H2
Hydrogen Replacement +4 +2
TiCl4 + 2Mg Ti + 2MgCl2
Metal Replacement -1 -1
Cl2 + 2KBr KCl + Br2
Halogen Replacement

24. Types of Single-Replacement Reactions+2 +1
Sr + 2H2O Sr(OH)2 + H2
Hydrogen Replacement +4 +2
TiCl4 + 2Mg Ti + 2MgCl2
Metal Replacement -1 -1
Cl2 + 2KBr KCl + Br2
Halogen Replacement
Note: In RED – the part of the compound replaced
Dr. Coarfa - Chem1305

25. The Activity Series for Metals
(given on the exam)
React with acids and cold water to form H2(g)
Hydrogen Displacement Reaction
M + BC AC + B
React with acids and steam to form H2(g)
M is metal
BC is acid or H2O
B is H2
React with acids to form H2(g);
no reaction with water
Ca + 2H2O Ca(OH)2 + H2
Pb + 2H2O Pb(OH)2 + H2
No reaction with water or acids
Dr. Coarfa - Chem1305

26. The Activity Series for Halogens
F2 > Cl2 > Br2 > I2
Halogen Displacement Reaction -1 -1
Cl2 + 2KBr KCl + Br2
I2 + 2KBr KI + Br2

27. Learning Check
Predict whether or not a reaction occurs for each of the following:
a. Aluminum foil is added to an iron(II) sulfate solution b. Iron wire is added to an aluminum sulfate solution.
c. Manganese metal is added to acetic acid d. Magnesium metal is added to water (cold).
Solution:
We refer to the activity series for the reactivity of each of the metals.
a. Aluminum precedes iron in the activity series: Al > Fe. Thus, a reaction occurs, and
Al displaces Fe from the solution.
b. Conversely, iron follows aluminum in the activity series: Al > Fe. Thus, there is no reaction.
c. Manganese precedes hydrogen in the activity series: Mn > (H). Thus, a reaction occurs, and
Mn produces H2 gas that bubbles from the solution.
d. Magnesium is not an active metal. Therefore, magnesium does not react with water, and
there is no reaction.
Practice Exercise
a. A gold ring is dropped into sulfuric acid b. A zinc granule is dropped into hydrochloric acid.
c. A cadmium foil is put into a lead(II) nitrate solution. d. A chromium strip is put into water.

28. Learning Check
Write a balanced chemical equation for each of the following single-replacement reactions:
a. Nickel metal is placed in a tin(II) sulfate solution b. Cobalt metal is put in a cadmium nitrate solution.
c. Manganese chips are added to sulfuric acid d. A chunk of potassium is dropped into water.
Solution:
First, we will refer to the activity series for the relative positions of each of the metals. Then we will write the equations.
a. Nickel is above tin in the activity series: Ni > Sn. Therefore, a reaction occurs and Ni displaces Sn from the solution.
Ni(s) + SnSO4(aq) → NiSO4(aq) + Sn(s)
b. Cobalt is below cadmium in the series: Cd > Co. Therefore, there is no reaction.
Co(s) + Cd(NO3)2(aq) → NR
c. Manganese is above hydrogen in the series: Mn > (H). Therefore, a reaction occurs, and Mn releases H2 gas bubbles from the solution.
Mn(s) + H2SO4(aq) → MnSO4(aq) + H2(g)
d. Potassium is a Group IA/1 active metal. Therefore, a reaction occurs, and K releases H2 gas from the solution.
2 K(s) + 2 H2O(l) → 2 KOH(aq) + H2(g)
Practice Exercise
a. Nickel metal is placed in a silver nitrate solution b. Gold metal is placed in a silver nitrate solution.
c. A chunk of cadmium metal is dropped into hydrochloric acid d. A small piece of calcium metal is dropped into water.

29. Double Replacement In a double replacement,
two elements in the reactants exchange places.
AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)
ZnS(s) HCl(aq) ZnCl2(aq) + H2S(g)

30. Solubility Rules
Not all ionic compounds are soluble in water. We can use the solubility rules to predict if a compound will be soluble in water.
(given on the exam)
Dr. Coarfa - Chem1305

31. Learning Check
Write a balanced chemical equation for each of the following double-replacement reactions.
a. Aqueous barium chloride is added to a potassium chromate solution.
b. Aqueous strontium acetate is added to a lithium hydroxide solution.
Solution:
For double-replacement reactions, we switch anions for the two compounds and check the solubility rules for an insoluble compound.
a. Barium chloride and potassium chromate give barium chromate and potassium chloride. According to solubility Rule 7, we find that barium chromate is insoluble. The balanced equation is
BaCl2(aq) + K2CrO4(aq) → BaCrO4(s) + 2 KCl(aq)
b. Strontium acetate and lithium hydroxide react as follows:
Sr(C2H3O2)2(aq) + 2 LiOH(aq) → Sr(OH)2(aq) + 2 LiC2H3O2(aq)
However, the solubility rules indicate that Sr(OH)2 and LiC2H3O2 are soluble.
Therefore, the equation is written Sr(C2H3O2)2(aq) + LiOH(aq) → NR
Practice Exercise
Write a balanced chemical equation for each of the following double-replacement reactions:
a. Aqueous zinc sulfate is added to a sodium carbonate solution.
b. Aqueous manganese(II) nitrate is added to a potassium hydroxide solution.

32. Neutralization Reactions
A neutralization reaction is the reaction of an acid and a base.
HX + BOH → BX + HOH
A neutralization reaction produces a salt and water.
H2SO4(aq) + 2 KOH(aq) → K2SO4(aq) + 2 H2O(l)
HNO3(aq) + NH4OH(aq) → NH4NO3(aq) + H2O (l)
Practice Exercise
Write a balanced chemical equation for each of the following neutralization reactions:
a. Chloric acid neutralizes a strontium hydroxide solution.
b. Phosphoric acid neutralizes a sodium hydroxide solution.

33. Learning Check Classify the following reactions as
1) single replacement or 2) double replacement.
A. 2Al(s) + 3H2SO4(aq) Al2(SO4)3(s) + 3H2(g)
B. Na2SO4(aq) + 2AgNO3(aq) Ag2SO4(s) + 2NaNO3(aq)
C. 3C(s) + Fe2O3(s) Fe(s) CO(g)

34. Solution Classify the following reactions as
1) single replacement or 2) double replacement.
1 A. 2Al(s) + 3H2SO4(aq) Al2(SO4)3(s) H2(g)
2 B. Na2SO4(aq) + 2AgNO3(aq) Ag2SO4(s) + 2NaNO3(aq)
1 C. 3C(s) + Fe2O3(s) Fe(s) CO(g)

35. Learning Check
Identify each reaction as 1) combination, 2) decomposition,
3) single replacement, or 4) double replacement.
A. 3Ba(s) + N2(g) Ba3N2(s)
B. 2Ag(s) + H2S(aq) Ag2S(s) + H2(g)
C. SiO2(s) + 4HF(aq) SiF4(s) + 2H2O(l)
D. PbCl2(aq) + K2SO4(aq) KCl(aq) + PbSO4(s)
E. K2CO3(s) K2O(aq) + CO2(g)

36. Solution 1 A. 3Ba(s) + N2(g) Ba3N2(s)
3 B. 2Ag(s) + H2S(aq) Ag2S(s) + H2(g)
4 C. SiO2(s) + 4HF(aq) SiF4(s) + 2H2O(l)
4 D. PbCl2(aq) + K2SO4(aq) KCl(aq) +PbSO4(s)
2 E. K2CO3(s) K2O(aq) + CO2(g)

37. Learning Check
Each of the following reactions occur in the formation of
smog or acid rain. Identify the type of reaction and
balance each.
A. NO(g) + O2(g) NO2(s)
B. N2(g) + O2(g) NO(g)
C. SO2(g) + O2(g) SO3(g)
D. NO2(g) NO(g) + O(g)

38. Solution Each of the following reactions occur in the formation of
smog or acid rain. Identify the type of reaction and
balance each.
Combination
A. 2NO(g) + O2(g) NO2(s)
B. N2(g) + O2(g) 2NO(g)
C. 2SO2(g) + O2(g) SO3(g)
Decomposition
D. NO2(g) NO(g) + O(g)

39. Review Chapter 7 1. Physical changes vs. chemical changes
2. Chemical reactions. Chemical equations: definition, symbols, balancing
3. Types of reactions:
- combination;
- decomposition;
- single replacement (activity series of metals and halogens);
- double replacement
- neutralization 39