1. Chapter 9
Chemical Reactions

2. Physical Change In a physical change,
The identity and composition of the substance do not change
The state can change or the material can be torn into smaller pieces
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3. Chemical Change In a chemical change,
Reacting substances form new substances with different compositions and properties
A chemical reaction takes place
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4. Chemical Reaction In a chemical reaction,
Old bonds are broken and new bonds are formed
Atoms in the reactants are rearranged to form one or more different substances
Fe and O2 form rust (Fe2O3)

5. Chemical Reaction In a chemical reaction,
A chemical change produces one or more new substances
There is a change in the composition of one or more substances
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6. Evidence of a Chemical Reaction
Changes that can be seen are evidence of a chemical reaction.
Table 9.2

7. Writing a Chemical Reaction
Chemists use a shorthand approach when writing the specifics of a chemical reaction. This approach is called the chemical equation.
Reactants -----> Products

8. Chemical Equations A chemical equation,
Gives the chemical formulas of the reactants on the left of an arrow and the products on the right
Reactants Product
O2 (g)
CO2 (g)
C(s)

9. Symbols Used in Equations
Symbols used in chemical
equations show:
The states of the reactants
The states of the products
The reaction conditions
Table 9.3
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10. Chemical Equations Are Balanced
In a balanced chemical reaction,
Atoms are not gained or lost

11. Chemical Equations Are Balanced
In a balanced chemical reaction,
The number of reactant atoms are equal to the number of product atoms

12. Chemical Equations Chemical equations: symbolic descriptions of
chemical reactions.
Two parts to an equation:
reactants and products
H2 + O2  H2O
A Chemical Equation must also be balanced.
2H2 + O2 --> 2H2O

13. Balanced Chemical Equations
Chemical Equations must be balanced
There must be equal numbers of atoms of each element on both sides of the equation (both sides of the arrow)
1. Write the correct symbols and formulas for all of the reactants and products.
2. Count the number of each type of atom on BOTH sides of the equation.
3. Insert coefficients until there are the equal numbers of each kind of atom on both sides of the equation.

14. A Balanced Chemical Equation
Al S Al2S Not Balanced
coefficients
2Al S Al2S3 Balanced
2 Al = Al
3 S = S

15. Learning Check P4(s) + 6 Br2(l) → 4 PBr3(g)
State the number of atoms of each element on the
reactant and on the product sides of the equations:
P4(s) Br2(l) → 4 PBr3(g)

16. Learning Check 2Al(s) + Fe2O3(s) → 2Fe(s) + Al2O3(s)
State the number of atoms of each element on the
reactant and on the product sides of the equations:
2Al(s) + Fe2O3(s) → 2Fe(s) + Al2O3(s)

17. Learning Check Check the balance of atoms in the following:
P-1
Check the balance of atoms in the following:
Fe3O4(s) H2(g) Fe(s) H2O(l)
1. Number of H atoms in reactants.
A) 2 B) 4 C) 8
2. Number of O atoms in reactants.
3. Number of Fe atoms in reactants.
A) 1 B) 3 C) 4

18. Learning Check Determine if each equation is balanced or not.
Na(s) + N2(g) → NaN3(s)
C2H4(g) H2O(l) → C2H5OH(l)

19. Balancing Equations
Methane reacts with oxygen (combustion reaction) to form carbon dioxide and water.
Write a properly balanced chemical equation
1. Write out chemical formulas
CH O2  CO H2O
2. Use coefficients to balance the equation

20. The Numbers in Chemical Equations

21. More Practice: Balancing Reactions
C2H O2  CO H2O
C3H O2  CO H2O
NH O2  NO H2O

22. And more practice….
B2H H2O  H3BO H2
C3H8O O2  CO H2O

23. Balancing with Polyatomic Ions
MgCl2(aq) + Na3PO4(aq) NaCl(aq) + Mg3(PO4)2(s)
HINT: Balance PO43- as a unit.

24. Review of steps to balance a chemical equation.
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25. In Class QUIZ 6.1 1. __Mg(s) + __N2(g) __Mg3N2(s)
Balance each equation and list the coefficients in the balanced equation going from reactants to products:
1. __Mg(s) + __N2(g) __Mg3N2(s)
A) 1, 3, B) 3, 1, C) 3, 1, 1
2. __Al(s) + __Cl2(g) __AlCl3(s)
A) 3, 3, 2 B) 1, 3, C) 2, 3, 2

26. In Class QUIZ 6.2
Balance and list the coefficients from reactants to products:
3. __Fe2O3(s) __C(s) __Fe(s) __CO2(g)
A) 2, 3, 2, B) 2, 3, 4, C) 1, 1, 2, 3
4. __Al(s) + __FeO(s) __Fe(s) __Al2O3(s)
A) 2, 3, 3, B) 2, 1, 1, C) 3, 3, 3, 1
5. __Al(s) + __H2SO4(aq) __Al2(SO4)3(aq) + __H2(g)
A) 3, 2, 1, B) 2, 3, 1, C) 2, 3, 2, 3

27. Chapter 9 Types of Reactions
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28. Type of Reactions Chemical reactions can be classified as
Combination reactions.
Decomposition reactions.
Single Replacement reactions.
Double Replacement reactions.
Combustion reactions.

29. 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 A B

30. Decomposition In a decomposition reaction,
One substance splits into two or more simpler substances.
2HgO(s) Hg(l) + O2(g)
2KClO3(s) KCl(s) + 3O2(g)
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31. Learning Check Classify the following reactions as
A) combination or B) decomposition:
1. H2(g) + Br2(g) HBr(l)
2. Al2(CO3)3(s) Al2O3(s) + 3CO2(g)
3. 4Al(s) + 3C(s) Al4C3(s) A B A

32. Single Replacement In a single replacement reaction,
One element takes the place of a different element in a reacting compound.
Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)
Fe(s) + CuSO4(aq) FeSO4(aq) + Cu(s)
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33. Double Replacement In a double replacement reaction,
Two elements in the reactants exchange places.
AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)
ZnS(s) HCl(aq) ZnCl2(aq) + H2S(g)
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34. Learning Check Classify the following reactions as
A) single replacement B) double replacement
1. 2Al(s) + 3H2SO4(aq) Al2(SO4)3(s) + 3H2(g)
2. Na2SO4(aq) + 2AgNO3(aq) Ag2SO4(s) + 2NaNO3(aq)
3. 3C(s) + Fe2O3(s) Fe(s) CO(g) A B A

35. Combustion In a combustion reaction,
A compound such as carbon reacts with oxygen, O2.
C(s) + O2(g) CO2(g)
CH4(g) + 2O2(g) CO2 (g) + 2H2O(g)
C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g)
Fuels burned in oxygen produce CO2, H2O, and energy.

36. Learning Check Balance the combustion equation
___C5H ___O ___CO2 + ___H2O

37. Summary of Reaction Types
Table 9.4
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38. Energy in Chemical Reactions
Chapter 9
Energy in Chemical Reactions
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39. Heat of Reaction The heat of reaction,
Is the amount of heat absorbed or released during a reaction at constant pressure.
Is the difference in the energy of the reactants and the products.
Is shown as the symbol ΔH.
ΔH = Hproducts − Hreactants

40. Endothermic Reactions
In an endothermic reaction,
Heat is absorbed.
The sign of ΔH is +.
The energy of the products is greater than the energy of the reactants.
Heat is a reactant.
N2(g) + O2 (g) kJ NO(g)
ΔH = +181 kJ (heat added)
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41. Exothermic Reactions In an exothermic reaction, Heat is released.
The sign of ΔH is -.
The energy of the products is less than the energy of the reactants.
Heat is a product.
C(s) + 2H2(g) CH4(g) + 75 kJ
ΔH = - 75 kJ (heat given off)
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42. Learning Check Identify each reaction as
1) exothermic or 2) endothermic.
A. N2 + 3H NH kJ
B. CaCO kJ CaO + CO2
C. 2SO2 + O2 2SO3 + heat