1. Chemical Equations and Reactions Chapter 8
General Chemistry
Ch. 8 Chemical Eq and React Gen Chem

2. Chemical Reactions Basics
Ch. 8 Chemical Eq and React Gen Chem

3. Chemical Reactions A chemical reactions are ______________________.
Recall: chemical changes are when one or more substances are changed into different substances
Examples: wood burning, metal rusting
Ch. 8 Chemical Eq and React Gen Chem

4. Indications of a Chemical Reaction
Certain easily observed changes indicate that a chemical reaction has occurred:
_______________by heat and/or light
color change
production of _________
production of __________
A solid that is produced as a result of a chemical reaction in solution and that separates from the solution is known as a precipitate
Ch. 8 Chemical Eq and React Gen Chem

5. Law of Conservation of Matter
Chemical reactions obey the Law of Conservation of Matter
in all chemical and physical changes, matter is neither created or destroyed
____________________________________________________________________
Ch. 8 Chemical Eq and React Gen Chem

6. Chemical Equations
A chemical equation represents, with symbols and formulas, the identities and the amounts of the reactants and products in a chemical reaction.
Has two parts:
Reactants: __________________________
Products: ____________________________
The reactants turn into the products
4 Fe O2  2 Fe2O3
Reactants  products
Ch. 8 Chemical Eq and React Gen Chem

7. Ways to Express a Chemical Reaction
The way atoms are joined is changed in a chemical reaction.
Can be described several ways:
1. In a sentence
Copper reacts with chlorine to form copper (II) chloride.
2. In a word equation
Copper + chlorine ® copper (II) chloride
3. In formula equation:
Cu + Cl2  CuCl2
Ch. 8 Chemical Eq and React Gen Chem

8. Symbols Used in Chemical Equations
Ch. 8 Chemical Eq and React Gen Chem

9. Additional Symbols Used in Equations
shows that heat is supplied to the reaction
is used to indicate a catalyst is supplied, in this case, platinum.
Ch. 8 Chemical Eq and React Gen Chem

10. What is a catalyst? A catalyst is _______________
___________________, without being changed or used up by the reaction.
Enzymes are biological or protein catalysts.
Ch. 8 Chemical Eq and React Gen Chem

11. Study Buddy Review
What are four things that indicate a chemical reaction has taken place?
What is the Law of Conservation of mass?
What does the symbol (l) mean?
What does (aq) mean?
Ch. 8 Chemical Eq and React Gen Chem

12. Balancing Chemical Equations
Ch. 8 Chemical Eq and React Gen Chem

13. Skeleton and Balanced Equations
_____________________do not indicate how many of each element/compound
_______________________the number of atoms of each element is the same on both sides of the reaction.
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14. Numbers in Balanced Equations
Use coefficients to balance equation
Coefficients: _______________________ ______________which represents number of units of that compound
Subscript: small whole number placed in chemical formula to represent number of atoms of an element in a compound
Ch. 8 Chemical Eq and React Gen Chem

15. 4 Fe + 3 O2  2 Fe2O3 subscript Coefficient
Ch. 8 Chemical Eq and React Gen Chem

16. Balanced Equation
A balanced equation has the _____________________ of each element on both sides of the equation
Atoms can’t be created or destroyed
All the atoms at the beginning must appear in the end
Ch. 8 Chemical Eq and React Gen Chem

17. ® O + C C O O C + O2 ® CO We need one more oxygen in the products.
Can’t change the formula, because it describes what it is (carbon monoxide in this example)
Ch. 8 Chemical Eq and React Gen Chem

18. ® Must be used to make another CO But where did the other C come from?+ C O C O
Must be used to make another CO
But where did the other C come from?
Ch. 8 Chemical Eq and React Gen Chem

19. ® Must have started with two C 2 C + O2 ® 2 CO C C O O + O C C O
Ch. 8 Chemical Eq and React Gen Chem

20. Rules for balancing:
Assemble, write the correct formulas for all the reactants and products
Count the number of atoms of each type of element appearing on both sides
Balance the atoms of an element one at a time by adding coefficients (the numbers in front) - save H and O until LAST!
Check to make sure it is balanced.
Ch. 8 Chemical Eq and React Gen Chem

21. Never Never change a subscript to balance an equation.
If you change the formula you are describing a different reaction.
H2O is a different compound than H2O2
Never put a coefficient in the middle of a formula
2 NaCl is okay, Na2Cl is not.
Ch. 8 Chemical Eq and React Gen Chem

22. Balancing Equations Examples
H2 (g) + O2 (g)  H2O (l)
Zn + HCl  H ZnCl2
Pb (NO3) K2S  PbS + KNO3
Ch. 8 Chemical Eq and React Gen Chem

23. Word Equation Examples
Write a balanced chemical equation for the following:
Aqueous solutions of sulfuric acid and sodium hydroxide react to form aqueous sodium sulfate and water.
Ch. 8 Chemical Eq and React Gen Chem

24. Five General Types of Chemical Reactions
Ch. 8 Chemical Eq and React Gen Chem

25. Five General Types of Chemical Reactions
Synthesis (Composition)
________________________
Single-Replacement
Combustion
By knowing the type of reaction that is occurring, you can predict the products that will be formed.
Ch. 8 Chemical Eq and React Gen Chem

26. General Types of Chemical Reactions
Combination: A + B  AB
Decomposition: AB  A + B
Single Replacement :
AX +B  A + BX
Double Replacement:
AX + BY  AY + BX
Combustion:
CxHy + O2  CO2 + H2O

27. Synthesis (Combination)
General form: A + B  AB
____________________________
A, B = elements or compounds
AB = compound consisting of A and B
This is the only type of chemical reaction in which there is a single product formed. This single product is always more complex than the reactants.
Ch. 8 Chemical Eq and React Gen Chem

28. Examples of Synthesis Reactions
a. calcium + oxygen yields calcium oxide
2Ca + O2  2CaO
b. carbon dioxide + water yields carbonic acid
CO H2O  H2CO3
Notice: All equations show two (or more) reactants, but only one product.
Ch. 8 Chemical Eq and React Gen Chem

29. Decomposition Reactions
(Decomposing = breaking down into smaller parts; microorganisms)
_______________________________
______________________________The opposite of direct combination/synthesis.
You can identify this reaction because there is only one reactant.
General form: AB  A + B
AB = compound
A, B = elements or simpler compounds
Ch. 8 Chemical Eq and React Gen Chem

30. Examples of Decomposition Reactions
Water yields hydrogen and oxygen
2H2O  H O2
marble (rock) yields (with heating) calcium oxide and carbon dioxide
CaCO  CaO CO2
Notice: single compound decomposes into two (or more) products.
Ch. 8 Chemical Eq and React Gen Chem

31. Single-Replacement Reactions
__________________________________________________________
General Form: A + BX  AX + B
AX, BX = ionic compounds
A, B = elements
X = ion that switches partners
Ch. 8 Chemical Eq and React Gen Chem

32. Examples of Single-Replacement Reactions
Magnesium metal and copper (II) sulfate
Mg + CuSO4  MgSO4 + Cu
Iron metal and copper (II) sulfate)
Fe + CuSO4  FeSO4 + Cu
Ch. 8 Chemical Eq and React Gen Chem

33. Double-Replacement Reactions
______________________________________________________________
Look for: 2 compounds as reactants and 2 compounds as products.
Reactants are usually ionic compounds.
Specific example: neutralization reactions between acid and base
General form: AX + BY  AY + BX
(Notice: X and Y “change partners”)
Ch. 8 Chemical Eq and React Gen Chem

34. Examples of Double Replacement Reactions
Calcium carbonate and hydrochloric acid yield calcium chloride and carbonic acid.
CaCO3 + 2HCl  CaCl2 + H2CO3
Ch. 8 Chemical Eq and React Gen Chem

35. Rules of Double-Displacement Reactions
Reactants must be dissolved in water (releasing the ions).
Will occur if:
______________________________
_____________________
Ch. 8 Chemical Eq and React Gen Chem

36. C2H5OH (gasohol) + 3O2  3H2O + 2CO2
Combustion Reactions
Reactants: a fuel (usually a hydrocarbon) and oxygen.
Products: water, carbon dioxide, and lots of energy! (heat, light)
Examples:
CH4 (methane) + 2O2  2H2O + CO2
C2H5OH (gasohol) + 3O2  3H2O + 2CO2
Ch. 8 Chemical Eq and React Gen Chem

37. Study Buddy Review Describe each of the following to your study buddy:
Synthesis (combination)
Decomposition
Single-Replacement
Double-Replacement
Combustion
Ch. 8 Chemical Eq and React Gen Chem

38. Activity Series
Ch. 8 Chemical Eq and React Gen Chem

39. Activity Series and Single Replacement Reactions
Al + CuCl2  ???
Cu + AlCl3  ???
Only one of the following reactions will occur
How do you know which one?
Ch. 8 Chemical Eq and React Gen Chem

40. Activity Series of Metals
Ch. 8 Chemical Eq and React Gen Chem

41. Ch. 8 Chemical Eq and React Gen Chem

42. Activity Series Rules Elements at top of series are most active
Elements at bottom of series are least active (coinage metals)
__________________________________________________________
Example: Al + CuCl2  will occur
Cu + AlCl3  will NOT occur
Ch. 8 Chemical Eq and React Gen Chem

43. Activity Series Examples
Using the activity series, predict whether each of the possible reactions will occur:
Cr + H2O 
Pt + O2 
Cd + 2HBr 
Ch. 8 Chemical Eq and React Gen Chem

44. References Dr. Stephen L. Cotton Charles Page High School Mrs. Lijek
Ch. 8 Chemical Eq and React Gen Chem