1. Chapter 8
Chemical Reactions

2. 8.1 What Is a Chemical Reaction?
One or more substance(s) are converted into new substances.
Reactants are the starting materials.
Products are the newly created substances.

3. 8.1 What Is a Chemical Reaction?
Chemical equation
Showing a chemical reaction
Reactants are on the left.
Products on the right.
 means “react to form” or “Yields”
Reactants  Products

4. 8.2 Reactants Transformed into Products?
Consider the reaction:
H2 + I2  2HI
The reactants’ chemical and physical properties change! HI is not at all like H2 or I2

5. 8.3 Balancing Chemical Equations
Balanced chemical reaction
Shorthand method representing a reaction
H2 + I2  HI
But the number and type of atoms must be the same on both sides of an equation
Obey the Law of Conservation of Matter
Does this equation obey?

6. 8.3 Balancing Chemical Equations
Balancing equations
Balance by placing coefficients before reactants and products:
H2 + I2  HI H2 + I2  2HI
Reactants: 2H and 2I H and 2I
Products: 1H and 1I H and 2I

7. 8.3 Balancing Chemical Equations
What about 2H2 + 2I2  4HI?
Sorry 
Use smallest whole numbers as coefficients!
H2 + I2  2HI

8. 8.3 Balancing Chemical Equations
One more thing: Never balance equations using subscripts!
Changing the subscript changes the compound…a balancing “no-no”!

9. 8.2 Reactants Transformed into Products?
Reaction between molecules
Molecules collide with enough speed and at the correct angle to break reactant bonds!
Energy is absorbed (endothermic)
Energy is released when those bonds reform! (exothermic)

10. 8.4 Types of Reactions
Reaction types: each of these reactions is classified based on how the reactants form the products…
Single-replacement reaction
Double-replacement reaction
Decomposition reaction
Combination reaction
Combustion reaction
Acid/Base reaction

11. 8.4 Types of Reactions Single-replacement reaction
An element replaces different one in a compound:
The single element MUST BE more reactive than the element it replaces
Al is more reactive than Fe
2 Al + Fe2O3  Al2O3 + 2 Fe
Double-replacement reaction
Elements replace each other in two compounds:
PCl3 + 3AgF  PF3 + AgCl

12. Decomposition reaction
8.4 Types of Reactions
Decomposition reaction
One compound breaks down to two or more substances
One reactant, multiple products
2HgO(s)  2Hg(l) + O2(g)
Combination (aka addition/synthesis)
Two or more reactants combine to give another substance. Multiple reactants, one product
H2(g) + I2(g)  2 HI(g)

13. 8.4 Types of Reactions

14. 8.4 Types of Reactions Combustion reaction
Reaction of substance with O2
“Burning”
Fits into the other classes also
Products are often (but not always) H2Oand CO2

15. Team Work Problems part 1!

16. 8.5 Part 2: Precipitation Reactions
Precipitation reaction (double replacement)
Solid product forms from mixing two or more solutions
The solid that forms is the precipitate:
Ca(NO3)2(aq)+ 2NaF(aq)  2NaNO3(aq)+ CaF2(s)
The reactant salts are both soluble in water
CaF2 is INSOLUBLE in water so precipitates!
PPT “drop out” because they don’t dissolve

17. 8.5 Solubility and Precipitation Reactions
Dissociation
This is what happens when compounds dissolve
Ionic crystal lattice breaks apart into + and - ions
Covalent crystals separate into discrete molecules
NaCl(aq) means the
crystal dissociated
into Na+(aq) and Cl-(aq)
The ions are spread
throughout the mixture!
Dissociation Animation

18. 8.5 Solubility and Precipitation Reactions
Dissociation
C6H12O6(aq) means the molecular crystal breaks
into separate molecules
The molecules are spread throughout the mixture!
Dissociation Animation

19. 8.5 Solubility and Precipitation Reactions
Mass of a substance that dissolves in water at a particular temperature
Some molecular compounds dissolve in water
Polar molecules that are similar to water…
HCl and NH3 are examples
Most molecules are not very soluble in water
Many ionic compounds dissolve in water
Since they are composed if charged ions and therefore polar..but not all do!
Solubility rules tell which ones are soluble!

20. 8.5 Solubility and Precipitation Reactions
ANY compound with these is soluble!
PbCl2 BaSO4
NOT SOLUBLE

21. 8.5 Solubility and Precipitation Reactions
Double Replacement...is there a precipitate?
Pb(NO3) 2(aq) + NaI(aq)  PbI2 + NaNO3
-Balance the equation first and find out!

22. 8.5 Solubility and Precipitation Reactions
BALANCED Equation
Pb(NO3) 2(aq) + 2NaI(aq)  PbI2(s) + 2NaNO3(aq)
Is either product insoluble?(check rules)
NaNO3 is soluble so it stays (aq)
PbI2 is Insoluble (iodide salt of lead!)
PbI2 is INSOLUBLE so it precipitates…(S)
This is a precipitate reaction!
Lead iodide reaction

23. 8.5 Ionic and Net Ionic Equations
Full Equation
Pb(NO3) 2(aq) + 2NaI(aq)  PbI2(s) + 2NaNO3(aq)
Complete ionic equation…
Pb2+(aq) + 2 NO3- (aq) + 2 Na+(aq) + 2 I- (aq)  PbI2(s) + 2 Na+(aq) + 2 NO3-(aq)
Identify Spectator IONS and cancel out!
Write the NET ionic equation with what’s left:
Pb2+(aq) + 2 I- (aq)  PbI2(s)
PbI2 is INSOLUBLE so it precipitates!

24. 8.5 Solubility and Precipitation Reactions
A solution of sodium sulfate is combined with a solution of barium chloride. Does a precipitate form?
Follow the example and figure it out:
Write equation and balance it
Determine if one product is insoluble
Write full ionic equation
Write net ionic equation
Identify the ppt.

25. 8.5 Solubility and Precipitation Reactions
A solution of sodium sulfate is combined with a solution of barium chloride. Does a precipitation reaction occur?
YES: Ba2+(aq) + SO42-(aq)  BaSO4(s)

26. 8.6 Introduction to Acid−Base Reactions
Substance that dissociates H+(aq)
Examples: HCl (shown below) and HF

27. 8.6 Introduction to Acid−Base Reactions
Substance that dissociates OH-(aq)
Examples include NaOH, KOH, and Ca(OH)2.

28. 8.6 Introduction to Acid−Base Reactions
Acid-base neutralization
Acid + Base  a salt + water
HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)
Net ionic equation
H+(aq) + OH-(aq)  H2O(l)

29. 8.6 Introduction to Acid−Base Reactions
Determine the neutralization products of the reaction between chlorous acid and sodium hydroxide…
Balance full equation
Write full and net ionic equations

30. 8.6 Introduction to Acid−Base Reactions
Determine the neutralization products of the reaction between chlorous acid and sodium hydroxide…
Balance full equation
Write full and net ionic equations
HClO2(aq) + NaOH(aq)  NaClO2 (aq) + H2O(l)
Net ionic equation
H+(aq) + OH-(aq)  H2O(l)