1. Unit 10: Chemical Equations

2. 1. To learn to write chemical equations
Chapter Objectives
1. To learn to write chemical equations
2. To correctly interpret chemical equations
3. To balance chemical equations

3. 4. To classify chemical reactions
Chapter Objectives
4. To classify chemical reactions
5. To predict products of chemical reactions
6. To write ionic and net ionic equations

4. The original substances present are called REACTANTS
Chemical Reactions
In a chemical reaction, substances join together to form new substances
The original substances present are called REACTANTS
The new substances formed are called PRODUCTS

5. Discussion of Chemical Reactions
The general form of an equation is:
Reactants  Products
The  is read as “yields” or “reacts to produce”

6. Discussion of Chemical Reactions
A + B  C
Substance “A” and “B” react to produce substance “C”

7. Additional Symbols in Chemical Reactions
+ used to separate reactants or products
(s) means chemical is in solid state
(l) means chemical is in liquid state

8. Additional Symbols in Chemical Reactions
(g) means chemical is in gas state
(aq) means chemical is dissolved in water
*See Table 10-1 in book (page 278)

9.  means something is added to the reaction Usually this is heat
Other Symbols
 means something is added to the reaction
Usually this is heat
Pt means a catalyst (Pt) is added

10. Skeleton (Formula) Equation- the rough form of an equation
Skeleton Equations
Skeleton (Formula) Equation- the rough form of an equation
It only shows the framework for the chemical reaction

11. Write Skeleton Equations
Sodium metal reacts with Oxygen gas to form solid Sodium Oxide
Solid sulfur reacts with Fluorine gas to form gaseous Sulfur Hexafluoride when heated
Nitrogen reacts with Hydrogen to form Ammonia (NH3) gas. Heat is required.

12. Review-Write Skeleton Equations
1. Magnesium metal reacts with Chlorine to form solid Magnesium Chloride.
2. Aqueous Silver Nitrate reacts with aqueous Sodium Chloride to form solid Silver Chloride and aqueous sodium nitrate
Begin 3rd , 4th, & 5th, 7th

13. Law of Conservation of Mass
The Law of Conservation of Mass states that mass is neither created or destroyed in a chemical reaction
Because of this Law, it is necessary to balance chemical equations
Begin 1st, 3rd, 5th, & 7th

14. Balancing Chemical Equations
In balanced chemical equations, each side of the equation has the same number of atoms of each element
Coefficients are used to balance chemical equations

15. Question What is the difference between a coefficient and subscript?
Coefficients are written before the formulas
Subscripts are part of the formula
Never use SUBSCRIPTS to balance an equation!!

16. Rules for Balancing Equations
1. Determine the correct formulas for the reactants and products
2. Write the formulas for the reactants on the left side of the arrow. Write the formulas for the products on the right side of the arrow
Begin 3rd 1/18/02, 4th, & 5th

17. 5. Check to make sure each atom is balanced
Rules Continued
3. Count the number of atoms of each element present on both sides of the equation
4. Balance the elements one at a time by placing coefficients in front of the formula.
5. Check to make sure each atom is balanced

18. **If no coefficient is written, the coefficient is assumed to be “1”
Additional Rules
6. Check to make sure that all coefficients are in the lowest possible ratio
**If no coefficient is written, the coefficient is assumed to be “1”

19. Na (s) + Br2 (g)  NaBr (aq)
Examples
Balance the following
H2 (g) + O2 (g)  H2O (l)
Na (s) + Br2 (g)  NaBr (aq)
AgNO3 (aq) + Cu(s)  Cu(NO3)2 (aq) + Ag(s)
Begin 3rd , 4th, 5th

20. Classwork
Complete Worksheet

21. Review-balance the following
1. Fe + O2  Fe2O3
2. Al2O3 + H2  Al + H2O

22. Begin 4th & 5th Periods 1. FeCl3 + NaOH  Fe(OH)3 + NaCl
Quiz Review - Balance
1. FeCl3 + NaOH  Fe(OH)3 + NaCl
2. CuCl2 + NaI  CuI2 + NaCl
3. H2O2  H2O + O2
Begin 4th & 5th Periods

23. QUIZ
1) C6H6 + O2  CO2 + H2O
2) Mg + O2  MgO

24. 1. Solid sulfur reacts with gaseous fluorine to produce aqueous sulfur hexafluoride
2. Magnesium metal reacts with chlorine gas to make solid magnesium chloride
QUIZ REVIEW

25. Begin 4th & 5th Periods Pb(NO3)2 + 2 NaOH  Pb(OH)2 + 2 NaNO3
Additional Questions
Pb(NO3)2 + 2 NaOH  Pb(OH)2 + 2 NaNO3
How many oxygen atoms are on the reactant side?
How many oxygen atoms are in 2 NaNO3?
Begin 4th & 5th Periods

26. Balancing Equations - Determining Formulas
To Balance Equations, you must remember how to write correct chemical formulas
Begin 4th & 5th Periods

27. Example
Write the balanced equation for solid aluminum reacting with oxygen gas to form solid aluminum oxide
**Remember that the diatomic elements (Mr. BrINClHOF) appear with a subscript of two when alone

28. Additional Examples
1. Carbon reacts with Chlorine to form Carbon Tetrachloride
2. Magnesium metal reacts with solid Zinc (II) Carbonate to form solid Magnesium Carbonate and Zinc metal
3. Nitrogen gas reacts with Hydrogen gas to form Ammonia (NH3) gas
Begin 3rd 1/24/01

29. There are five general types of reactions: Synthesis Decomposition
Single Displacement
Double Displacement
Combustion
Begin 3rd , 4th, 5th, & 7th

30. Synthesis reactions are also called combination reactions
A synthesis reaction occurs when two substances combine to form a new compound
Begin 5th

31. Synthesis Reaction Continued
The general form of a synthesis reaction is:
A X  AX
Substance “AX” is the only substance formed
Begin 4th 1/25/02

32. Examples of Synthesis Reactions
2 Mg (s) + O2 (g)  2 MgO (s)
Fe (s) + Cl2 (g)  FeCl2 (s)
U (s) + 3 F2 (g)  UF6 (g)
Begin 4th & 5th

33. Decomposition Reaction
In decomposition reactions, one substance breaks down (decomposes) into two or more simpler substances
Begin 1st

34. Decomposition Reactions Cont.
General Form of Decomposition Reaction:
AX  A + X

35. Examples of Decomposition Reactions
2 HgO (s)  2 Hg (l) + O2 (g)
Ca(OH)2  CaO (s) + H2O (g)
H2SO4 (aq)  SO3 (g) + H2O (l) 

36. Write Correct Balance Equations
1. The synthesis of KCl
2. The decomposition of magnesium oxide
3. The decomposition of hydrogen peroxide (H2O2) into oxygen and water
Begin 3rd

37. Write Correct Balance Chemical Equations for the following reactions
1. The synthesis of barium fluoride
2. The decomposition of Mg(OH)2 into magnesium oxide and water
3. The decomposition of water
Begin 3rd

38. Review-Write Balanced Equations
1. Gaseous hydrogen reacts with gaseous chlorine to form aqueous hydrogen chloride
2. Carbon monoxide gas reacts with gaseous oxygen to form solid carbon dioxide

39. Write balanced equations
1. The synthesis of Iron (III) oxide
2. The decomposition of cobalt (IV) oxide
3. The decomposition of calcium hydroxide into calcium oxide and water
Begin 4rd 1/25/01

40. Write Balanced Equations
1) Na + Cl2 
2) HgCl2 
3) Fe(OH)3 

41. Single Replacement Reaction
In a single replacement reaction (also called a displacement reaction), an element reacts with a compound
A + BX  AX + B
Begin 4th & 5th 1/27/02

42. Examples of Single Replacement Reactions
Mg + Zn(NO3)2  Mg(NO3)2 + Zn
Mg + 2 AgNO3  Mg(NO3)2 (aq) + 2 Ag

43. Rules for Single Replacement Reactions
Not all single replacement reactions occur
You can determine if a reaction will occur by knowing the activity series of metals (See Handout)
Begin 3rd 1/28/02

44. Rules for Single Replacement
The activity series tell you if one metal can replace another metal in a reaction
The Activity Series is ordered
Any metal that is above another metal in the activity series WILL REPLACE the less reactive metal
Begin 3rd

45. Activity Series Li K Ca Na Mg Al Zn Fe Pb H* Cu Hg Ag

46. Predict if the following reactions will occur
1. Fe + H2O
2. Mg + LiNO3
3. Na + AgCl

47. Write balanced equations for the following reactions
1. Mg + O2 
2. FeCl3 
3. Fe + ZnO 
4. Br2 + MgI2 

48. Begin 4th, 1/29/02 Predict the products and balance: 1) Mg + O2 
Review
Predict the products and balance:
1) Mg + O2 
2) HCl 
3) Na + H2SO4 
4) Ag + ZnCl2 
Begin 4th, 1/29/02

49. Double Displacement Reactions
In a double displacement reaction, two compounds react
The compounds swap elements with each other
Begin 4th, 1/29/02

50. Double Displacement Cont
Compounds contain a positive and negative part
In a double displacement, the positive parts swap places with each other as do the negative parts

51. PbCl2 (s) + Li2SO4 (aq)  PbSO4 (s) + 2 LiCl (aq)
Examples
PbCl2 (s) + Li2SO4 (aq)  PbSO4 (s) + 2 LiCl (aq)
ZnBr2 (aq) + 2 AgNO3 (aq)  Zn(NO3)2 (aq) + 2 AgBr (s)

52. Predict the Products of the following reactions and balance
BaCl2 (aq) + KClO3 (aq) 
HCl (aq) + NaOH (aq) 
RbBr (aq) + AgCl (aq) 
Begin 3rd , 7th

53. The products are CO2 and H2O
Combustion Reactions
In a combustion reaction, a Hydrocarbon (compound containing Hydrogen and Carbon) reacts with Oxygen (O2)
The products are CO2 and H2O
Begin 1st

54. *Combustion Reactions commonly require large coefficients
Example
2 C6H O212 CO2 + 6 H2O
*Combustion Reactions commonly require large coefficients

55. Guided Practice
Write the balanced equation for the following combustion reactions:
a. C4H8
b. C6H12O6
c. C7H16
Begin 3rd , 4th, 7th

56. Independent Practice- Predict the products for the following reactions
1. Hf + N2  (Hf takes a +4 charge)
2. Mg + H2SO4 
3. C2H6 + O2 
4. Pb(NO3)2 + NaI 
5. Fe + O2  (Fe takes a +3 charge)
Begin 3rd, , 4th, 5th

57. For example: NaCl (aq) really looks like Na+(aq) and Cl- (aq)
Ionic Equations
Most ionic compound dissociate (or break apart) when dissolved in water to form its component ions
For example: NaCl (aq) really looks like Na+(aq) and Cl- (aq)

58. Soluble Vs. Precipitate
Soluble means that the compound breaks down into its ions in water
Ex) NaCl is soluble so it forms Na+ and Cl-
Insoluble means that the compound doesn’t break down in water

59. Precipitate Reactions
In double replacement reactions, often one of the product will be insoluble
The insoluble product is referred to as a precipitate

60. Practice Determine if soluble or insoluble: A) NaCl B) K2O
C) Fe(NO3)3 D) AgCl
E) BaS F) Cd(OH)2
G) FeCl3 H) PbCO3

61. Ionic Equations Continued
To write a Complete Ionic Equation:
Write the aqueous substances as ions (leave any substances in gas, liquids, & solids alone)
Example:
AgNO3 (aq) + NaCl (aq)  AgCl (s) + NaNO3 (aq)
Begin 3rd , 5th, 7th

62. Writing Ionic Equations
1. (NH4)2S (aq) + Cd(NO3)2 (aq)  NH4NO3 (???) + CdS (???)
2. Zn(NO3)2 (aq) + (NH4)2S (aq)  ZnS (???) + NH4NO3 (???)

63. Spectator Ions
Spectator Ions-Ions that are not directly involved in a reaction
Spectator ions show up on both sides of the equation
Spectator Ions cancel out
Begin 1st

64. The Net Ionic Equation does NOT include spectator ions
NET Ionic Equations
Net Ionic Equation-Indicate the particles that actually take part in a reaction
The Net Ionic Equation does NOT include spectator ions
Net Ionic Equations must be balanced according to atoms and charge

65. Write Net Ionic Equations
1. (NH4)2S (aq) + Cd(NO3)2 (aq) 
2. Zn(NO3)2 (aq) + (NH4)2S (aq) 