1. Chemical Equations
Pb(NO3)2 + 2 KI PbI2 + 2 KNO3

2. Chemical Reaction
A process in which at least one new substance is produced as a result of chemical change.

3. Evidence of Chemical Reactions
Formation of a precipitate (solid)
Production of gas
Unexpected color change
Heat, light, and/or flame is produced
Change in odor

4. Chemical Equations
Chemical reactions are expressed by chemical equations.
Chemical equations identify the reactants (starting chemicals) and the products (ending chemicals).
The reactants are always on the left side of the equation, and the products are on the right side.
Coefficients are used to show the molar ratios of the reactants and products.

5. Chemical Equations
coefficients
2H2 + O H2O
reactants
products

6. Learning Check
Identify the reactants, products, and the coefficients in the following examples: AgNO3 + NaCl AgCl + NaNO3 2 AB + 2 C2D 2 AD + 2 C2B

7. A Chemical Reaction
Reactants Products

8. Learning Check A. How does an equation indicate a change in
the identity of the reacting substances?
B. How did the yellow and pink reactants
combine?
C. Did all the reactants form product? How can you
tell?

9. Learning Check A. How does an equation indicate a change in
the identity of the reacting substances?
The formulas of the reactants are different
than the formulas of the products.
B. How did the yellow and pink reactants
combine? 1 yellow combined with 1 pink.
C. Did all the reactants form product? Why or
why not? No. There were more pink
reactants than yellow.

10. Writing a Chemical Equation
Chemical equations give a “before-and-after” picture of a chemical reaction
Reactants Products
MgO C CO Mg
magnesium oxide react to form carbon monoxide
plus carbon and magnesium

11. Reading A Chemical Equation
4 NH O NO H2O
Four molecules of NH3 react with five molecules O2 to produce four molecules NO and six molecules of H2O OR
Four moles NH3 react with 5 moles O2 to produce four moles NO and six moles H2O

12. Balanced Chemical Equations
Same numbers of each type of atom on each side of the equation
Al S Al2S Not Balanced
2Al S Al2S Balanced

13. Matter Is Conserved total reactant atoms = total product atoms
H Cl HCl
total reactant atoms = total product atoms
2H, 2Cl H, 2Cl
total reactant mass = total product mass
2(1.0) (35.5) (36.5)
73.0 g/mol = g/mol

14. Law of Conservation of Mass
Matter is neither created nor destroyed in a chemical reaction.
Matter can be changed from one form into another, mixtures can be separated or made, and pure substances can be decomposed, but the total amount of mass remains constant.
Whenever matter undergoes a change, the total mass of the products of the change is, within measurable limits, the same as the total mass of the reactants.

15. Balance Equations with Coefficients
Coefficients are used to balance each type of atom
4NH O NO + 6H2O
4 N = N
12 H = H
10 O = O

16. Learning Check Fe3O4 + 4 H2 3 Fe + 4 H2O A. Number of H atoms in 4 H2O
1) ) ) 8
B. Number of O atoms in 4 H2O
C. Number of Fe atoms in Fe3O4
1) ) ) 4

17. Learning Check Fe3O4 + 4 H2 3 Fe + 4 H2O A. Number of H atoms in 4 H2O
3) 8
B. Number of O atoms in 4 H2O
2) 4
C. Number of Fe atoms in Fe3O4
2) 3

18. Learning Check Balance each equation: A. Mg + N2 Mg3N2
B. Al Cl AlCl3
C. Al FeO Fe Al2O3

19. Learning Check Balance each equation: A. 3Mg + N2 Mg3N2
B. 2Al Cl AlCl3
C Al FeO Fe Al2O3

20. Reaction Types
Most chemical reactions can be placed into one of five basic types:
Synthesis
Decomposition
Single replacement
Double replacement
Combustion

21. Synthesis Reactions
Elements are joined together OR Compounds are joined together  
2H2 + O2 → 2H2O  

22. Decomposition Reactions
A compound breaks into parts.  
2H2O → 2H2 + O2

23. Single Replacement Reactions
A single element replaces an element in a compound.  
Zn + 2HCl → H2 + ZnCl2

24. Single Replacement Reactions (cont’d)
The number of dancers has not changed, but the lady switched her partner.
Note that like replaces like. In the example, a female will replace a female. In a chemical reaction, a cation will replace a cation.

25. Double Replacement Reactions
Two elements from two different compounds switch places.  
H2SO4 + 2NaOH → Na2SO4 + 2H2O

26. Double Replacement Reactions (cont’d)
Note that like replaces like. In the example, the men change hats. In a chemical reaction, a cation swaps with a cation, and an anion swaps with an anion.

27. Combustion Reactions
A hydrocarbon (a compound containing only carbon and hydrogen) combines with oxygen.  
The products of combustion are always carbon dioxide and water.  
hydrocarbon + oxygen → carbon dioxide + water  
CH4 + 2O2 → CO2 + 2H2O
Often gives off heat and light

28. Visual Summary of Reaction Types

29. Learning Check
Identify each type of reaction: a) 2NaBr + Ca(OH)2 2NaOH + CaBr2 b) P4 + 3O2 2P2O3 c) C3H6O + 4O2 3CO2 + 3H2O d) 2NO2 N2 + 2O2 e) Pb + FeSO4 Fe + PbSO4

30. Learning Check
Identify each type of reaction: a) 2NaBr + Ca(OH)2 2NaOH + CaBr2 Double replacement b) P4 + 3O2 2P2O3 Synthesis c) C3H6O + 4O2 3CO2 + 3H2O Combustion

31. Learning Check
Identify each type of reaction: d) 2NO2 N2 + 2O2 Decomposition e) Pb + FeSO4 Fe + PbSO4 Single Replacement

32. Equations with Polyatomic Ions
Polyatomic ions are ions composed of multiple atoms which are covalently bonded Examples: CO32- and NH4+ Often the polyatomic ions will remain unchanged during a reaction.

33. Writing Formulas with Polyatomic Ions
Polyatomic ions often have subscripts of their own, as in the SO42- ion. Parenthesis surround the formula of the polyatomic ion when there is more than one. Al2(SO4)3 NOT Al2SO43

34. Learning Check
How many Al, S, and O atoms are present in each of these formulas? Al2(SO4)3 Al2SO43 Al = Al = S = S = O = O =

35. Learning Check
How many Al, S, and O atoms are present in each of these formulas? Al2(SO4)3 Al2SO43 Al = 2 Al = 2 S = 3 S = 1 O = 12 O = 43

36. Learning Check
How many SO42- are present in the molecule Al2(SO4)3?

37. Learning Check
How many SO42- ions are present in the molecule Al2(SO4)3? There are 3 (SO42-) ions

38. Balancing Equations with Polyatomic Ions
When a polyatomic ion appears in both the reactants and the products (meaning it does not change during the reaction) it can be treated as an atom. 2Al(NO3)3 + 3H2SO4 → 6HNO3 + Al2(SO4)3 Treat (NO3-) as if it were an atom Treat (SO42-) as if it were an atom As always, use only the coefficients to balance the equation!

39. Learning Check
2Al(NO3)3 + 3H2SO4 → 6HNO3 + Al2(SO4)3 Al = Al = *NO3- = *NO3- = H = H = *SO42- = *SO42- = * Treated as an atom

40. Learning Check
2Al(NO3)3 + 3H2SO4 → 6HNO3 + Al2(SO4)3 Al = 2 Al = 2 *NO3- = 6 *NO3- = 6 H = 6 H = 6 *SO42- = 3 *SO42- = 3 *Treated as an atom

41. Learning Check Balance the following equations:
__NaHCO __Na2CO3 + __CO2 + __H2O
__Al2(SO4)3 + __Ca(OH) __Al(OH)3 + __Ca(SO4)

42. Learning Check Balance the following equation:
2NaHCO Na2CO3 + CO2 + H2O
Al2(SO4)3 + 3Ca(OH) Al(OH)3 + 3Ca(SO4)