1. Chapter 8 Chemical Reactions

2. Evidence of Chemical Change
Color change
Formation of a solid
Formation of a gas
Absorption or release of heat energy
Emission of light energy

3. Evidence of Chemical Change
Color change

4. Evidence of Chemical Change
Formation of a solid

5. Evidence of Chemical Change
Formation of a gas

6. Evidence of Chemical Change
Evolution of heat and light

7. Evidence of Chemical Change
Emission of light

8. Evidence of Chemical Change
Heat transfer as evidence
of physical change
Many physical changes are accompanied by heat transfer, so be cautious in using this form of evidence of a chemical change.

9. Evolution of a Chemical Equation
When solid potassium is added to liquid water, a reaction occurs, producing hydrogen gas, potassium hydroxide solution, and heat:

10. Evolution of a Chemical Equation
Chemists have developed a standardized shorthand
method for describing chemical reactions, such
as the reaction of sodium and water, in writing.
State Symbols and Their Meanings
Symbol Meaning
(s) solid
(l) liquid
(g) gas
(aq) aqueous (dissolved in water)

11. Evolution of a Chemical Equation
Solid potassium K(s)
plus +
liquid water H2O(l)
yields
hydrogen gas H2(g)
potassium hydroxide solution KOH(aq)

12. Evolution of a Chemical Equation
The equation
K(s) + H2O(l) H2(g) + KOH(aq)
is said to be unbalanced because the number of atoms of each element is not the same before and after the chemical change.
An equation is balanced when the number of atoms of each element is the same before and after the chemical change
2 K(s) + 2 H2O(l) H2(g) + 2 KOH(aq)

13. Interpreting Chemical Equations
The particulate-level interpretation of a chemical equation:
2 H2(g) + O2(g) H2O(g)
Two molecules of hydrogen react with one oxygen molecule
to form two water molecules.

14. Interpreting Chemical Equations
The particulate-level interpretation of a chemical equation:

15. Interpreting Chemical Equations
The molar-level interpretation of a chemical equation:
2 H2(g) + O2(g) H2O(g)
Two moles of hydrogen react with one mole of oxygen
to form two moles of water.

16. Writing Chemical Equations
Write the formulas of the given reactants to the left of an arrow and the formulas of the products to the right.
Balance the equation by adding coefficients, but do not change the qualitative description of the reaction by adding, removing, or altering any chemical formula.

17. Combination Reactions
Two or more substances combine to form a single product:

18. Combination Reactions
Example:
Potassium combines with oxygen to form potassium oxide.
Solution:
Write the qualitative description:
K + O K2O
Balance the O:
K + O K2O
Balance the K:
4 K + O K2O

19. Combination Reactions
Reactants: Any combination of elements and/or
compounds
Reaction type: Combination
Equation type: A + X AX
Products: One compound

20. Decomposition Reactions
A compound breaks down into simpler substances:

21. Decomposition Reactions
Example:
Water is decomposed into its elements.
Solution:
Write the qualitative description:
H2O (l)  H2 (g) O2 (g)
Balance the O:
2 H2O (l)  2 H2 (g) O2 (g)

22. Decomposition Reactions
Example:
Calcium carbonate (limestone) is decomposed into carbon dioxide and calcium oxide (lime).
CaCO3(s)  CaO (s) CO2 (g)

23. Decomposition Reactions
Reactants: One compound
Reaction type: Decomposition
Equation type: AX A + X
Products: Any combination of elements and
compounds

24. Single-Replacement Reactions
One element appears to replace another in a compound:

25. Single-Replacement Reactions
Example:
Potassium is able to replace hydrogen in water.
2 K(s) HOH (l)  H2 (g) KOH (aq)

26. Single-Replacement Reactions
Example:
A copper strip is placed in a solution of silver nitrate.
Solution:
Copper displaces silver from silver nitrate
Cu (s) + 2AgNO3 (aq)  Cu(NO3)2 (aq) + 2 Ag (s)
The reverse reaction does not occur

27. Single-Replacement Reactions
Example:
A magnesium strip is placed in a solution of hydrochloric acid.
Mg (s) + 2HCl (aq)  MgCl2 (aq) + H2 (g)
Magnesium displaces hydrogen from acid

28. Single-Replacement Reactions
Summary:
Single-Replacement Reactions
Reactants: Element (A) plus a solution of an acid
or an ionic compound (BX)
Reaction type: Single-replacement
Equation type: A + BX AX + B
Products: Element (B) must be less active than element A

29. Double-Replacement Reactions
Ions of two reactants appear to change partners:

30. Double-Replacement Reactions
Double-Replacement Reaction between two ionic compounds.
When solutions of two ionic compounds are mixed, positive ions from one compound may combine with negative ions from the other compound to form a solid (precipitate) or a molecular compound (water, weak acid, weak base, gas)

31. Formation of a precipitate
Formation of silver chloride precipitate from sodium chloride and silver nitrate.
NaCl (aq) AgNO3 (aq)  NaNO3 (aq) + AgCl (s)
Formation of barium sulfate precipitate from barium chloride and sodium sulfate.
BaCl2 (aq) + Na2SO4 (aq)  BaSO4 (s) NaCl (aq)

32. Neutralization Reactions: Formation of water
Neutralization reaction is a reaction between an acid and a base. One hydrogen ion from acid reacts with one hydroxide ion from a base to form one water molecule.
Neutralization of hydrochloric acid by sodium hydroxide.
HCl (aq) NaOH (aq)  NaCl (aq) H2O (l)
Reaction between sulfuric acid and solid aluminum hydroxide.
3 H2SO4 (aq) Al(OH)3 (s)  Al 2(SO4)3 (aq) H2O (l)

33. Formation of weak acid
Reaction of hydrochloric acid and sodium acetate to form acetic acid (weak acid)
HCl (aq) + NaCH3CO2 (aq)  NaCl (aq) + HCH3CO2 (aq)
Reaction between hydrochloric acid and sodium sulfide to form hydrosulfuric acid (weak acid)
Na2S(aq) HCl (aq)  2 NaCl (aq) + H2S (aq)

34. Na2CO3 (aq) + 2 HCl (aq)  2 NaCl (aq) + H2O(l) + CO2 (g)
Formation of a gas
Reaction between hydrochloric acid and sodium carbonate to form carbon dioxide gas
Na2CO3 (aq) HCl (aq)  2 NaCl (aq) + H2O(l) + CO2 (g)

35. Double-Replacement Reactions
Summary:
Double-Replacement Reactions
Reactants: Solutions of two ionic compounds,(AX + BY)
Reaction type: Double-replacement
Equation type: AX + BY AY + BX
Products: Two new compounds (AY + BX), one of which may be a solid, water, weak acid, weak base, or a gas

36. Summary

37. Homework
Homework: 9, 15, 19, 23, 27, 29, 31, 35, 39, 53, 59, 69, 76