1. Chapter 23
Chemical Reactions

2. 23.1 Forming New Substances
Chemical Reaction (Rxn): process in which one or more substances change to make one or more new substances
Chemical and physical properties of the new substance differ from those of the original
The combustion of fuel is an example of a chemical reaction

3. What are some signs of a chemical rxn?
Gas Formation

4. What are some signs of a chemical rxn?
Formation of a precipitate, or a solid in a solution

5. What are some signs of a chemical rxn?
Energy is released

6. What are some signs of a chemical rxn?
Color Change

7. Chemical Bonds Force that holds two atoms together in a molecule.
For a chemical rxn to take place, bonds must be broken and rearranged.
If molecules bump into each other with enough energy, bonds will break and atoms will be rearranged.

8. 23.2 Chemical Formulas and Equations
Chemical formulas use element symbols and subscripts to represent the number of atoms in a substance.
Chemical equations use formulas to describe a chemical rxn
Reactants = starting material
Products = ending material

9. Structure of an Equation
Reactant(s)  Product (s)
 means “yields”

10. Law of Conservation of Mass
Antoine Lavoisier
Matter is not created or destroyed during a chemical reaction
Nice hair!

11. Balancing Chemical Equations
The number of atoms on both sides of the chemical equation must be the same.
We must balance a chemical reaction to represent the law of conservation of mass.

12. Steps for balancing equations
Write the equation
Count the atoms
Use Coefficients to balance atoms (do not use the number 1 – if there is no coefficient the “1” is implied)
Note: Because of the Law of Definite Proportions, we cannot change subscripts without changing the type of chemical compound.
Check your work. Make sure the LCF’s are used as coefficients.

13. Practice Balancing Equations
1)____ AlBr3 + ____ K  ____ KBr + ___ Al
2)___ FeO + ___ PdF2  ___ FeF2 + __ PdO
3)____ P4 + ____ Br2  ____ PBr3
4)__ LiCl + ___ Br2  __ LiBr + ____ Cl2 
5)__ PbBr2 + __ HCl  __ HBr +_ PbCl2
6) __ CoBr3 + ___ CaSO4  __ CaBr2 + __ Co2(SO4)3
7) ____ Na3P + ____ CaF2  ____ NaF + ____ Ca3P2 
8) ____ Mn + ____ HI  ____ H2 + ____ MnI3
9) ____ Li3PO4 + ____ NaBr  ____ Na3PO4 + ____ LiBr
10)____ CaF2 + ____ Li2SO4  ____ CaSO4 + ____ LiF

14. Answers 1) 1 AlBr3 + 3 K  3 KBr + 1 Al
2) 1 FeO + 1 PdF2  1 FeF2 + 1 PdO
3) 1 P4 + 6 Br2  4 PBr3
4) 2 LiCl + 1 Br2  2 LiBr + 1 Cl2
5) 1 PbBr2 + 2 HCl  2 HBr + 1 PbCl2
6) 2 CoBr3 + 3 CaSO4  3 CaBr2 + 1 Co2(SO4)3
7) 2 Na3P + 3 CaF2  6 NaF + 1 Ca3P2
8) 2 Mn + 6 HI  3 H MnI3
9) 1 Li3PO4 + 3 NaBr  1 Na3PO4 + 3 LiBr
10) 1 CaF2 + 1 Li2SO4  1 CaSO4 + 2 LiF

15. 23.3 Types of Chemical Rxns
Synthesis: when 2 or more elements combine to form a more complex substance
A + B  AB

16. Types of Chemical Rxns
Decomposition: breaks down compounds into simpler substances
AB  A + B

17. Types of Chemical Rxns
Single Displacement (or single-replacement): When one element replaces another element in a compound
A + BC  AC + B

18. Reactivity of Elements
In a single-displacement rxn, a more reactive element can displace a less-reactive element in a compound.

19. Types of Chemical Rxns
Double Displacement (double replacement): When elements in one compound “trade places” with elements in another compound
AB + CD  AD + CB

20. Classify the following:
MgCO3 + 2HCl  MgCl2 + H2CO3
2H2O  2H2 + O2
4Fe + 3O2  2Fe2O3
2Na + 2H2O  2NaOH + H2
2KCl + Pb(NO3)2  2KNO3 + PbCl2
H2CO3  H2O + CO2
2Na + Cl2  2NaCl
Zn + 2HCl  ZnCl2 + H2

21. Answers
Double Replacement
Decomposition
Synthesis
Single Replacement

22. 23.4 Energy and Rates of Chemical Rxns

23. Energy and Reactions

24. Energy and Reactions

25. Energy and Reactions

26. Energy and Reactions
All chemical reactions need energy to get started.
The activation energy (Ea) is the minimum energy needed.
Sources of Ea:
Friction
Spark
Light
Heat

27. Energy and Reactions Endothermic Rxns Need Ea to start Absorb E
E of products > reactants
Exothermic Rxns
Need Ea to start
Release E
E of products < reactants

28. Endothermic Rxn

29. Exothermic Reaction

30. Rates of Chemical Rxns
Factors that can alter the rate (speed) of a reaction:
Surface Area of Reactants
Temperature
Concentration of Reactants
Catalysts and Inhibitors

31. If you dice the potatoes up smaller, they cook faster!
Surface Area
If you dice the potatoes up smaller, they cook faster!
If the reactants are more exposed to each other, the reaction happens faster!

32. Temperature
An increase in temperature causes an increase in kinetic energy, leading to more interaction of reactants and therefore a faster rate.

33. Concentration of Reactants

34. Catalysts and Inhibitors
Catalysts speed up reactions
A biological catalyst is called an enzyme
Inhibitors slow down reactions