1. Chemical Reactions
Chapter 7

2. Chemical Reactions
A CHEMICAL REACTION HAS OCCURRED IF THE SUBSTANCES AT THE END OF THE REACTION ARE DIFFERENT FROM THE SUBSTANCES AT THE START OF THE REACTION

3. Why is it important to balance equations?
What has to be true about the products and the reactants?

4. A Chemical Reaction
Reactants Products

5. Writing and Balancing Equations
A chemical equation is a shorthand expression for a chemical change or reaction.
word - equation : states in words
mercury (II) oxide + heat mercury + oxygen
bulky and cumbersome
2 HgO 2Hg + O2

6. Writing and Balancing Equations
General Format for Writing Equations
1. The reactants are separated from the products by an arrow that indicates the direction of the reaction.
2. The reactants are placed to the left and the products to the right of the arrow. A plus sign (+) is placed between reactants and between products when needed.

7. Writing and Balancing Equations
3. Conditions required to carry out the reaction may be placed above or below the arrow. A delta indicates heat is applied.
4. Coefficients 2 H2O are placed in front to balance the equation. One (1) is never placed there, it is just understood.

8. Writing and Balancing Equations
5. The physical state of a substance is indicated by the following symbols:
(s) solid (l) liquid (g) gaseous
(aq) aqueous: means water solution
yields reversible
reaction

9. Writing and Balancing Equations
Atoms cannot be created nor destroyed by normal chemical reactions.
This means we must have the same number and type of atoms in our products as we have in our reactants.
Reactants Products

10. Matter Is Conserved H2 + Cl2 2 HCl + + Total atoms = Total atoms
Total atoms = Total atoms
2 H, 2 Cl 2H, 2 Cl
Total Mass = Total Mass
2(1.0) (35.5) 2(36.5)
73.0 g = g

11. Writing and Balancing Equations
1. First you must have the equation in symbol format, you cannot balance a word equation.
2. Balancing:
a. Count and compare the number of atoms of each element on each side of the equation and determine those that must be balanced.

12. Writing and Balancing Equations
b. Balance each element one at a time, by placing whole numbers (coefficients) in front of the formulas containing the unbalanced element.
It is usually better to balance in this order: metals, nonmetals, hydrogen, oxygen.

13. Writing and Balancing Equations
A coefficient placed before a formula multiplies every atom in the formula by that number!
2H2SO4 = 4H’s 2S’s 8O’s
c. re-check each time you balance an element to see if anything else has become unbalanced. Make adjustments as needed.

14. Writing and Balancing Equations
d. Do a final check making sure that each element is balanced and that the smallest possible set of whole number coefficients has been used:
4HgO 4Hg + 2O2 incorrect
2HgO 2Hg + O2 correct

15. P r a c t i c e 1
NaOH Na2O + H2O
2NaOH Na2O + H2O
Fe + O Fe2O3
4Fe + 3O Fe2O3

16. P r a c t i c e 2
O2 + H H2O
O2 + 2H H2O
Cl2 + NaI NaCl + I2
Cl2 + 2NaI NaCl + I2

17. P r a c t i c e 3
CO2 + H2O C6H12O6 + O2
6CO2 + 6H2O C6H12O6 + 6O2
FeS + HCl FeCl2 + H2S
FeS + 2HCl FeCl2 + H2S

19. Turn in Balancing Activity worksheet
Balance the equations on the notes sheet.

20. P r a c t i c e 4 Al(NO3)3 + H2SO4 Al2(SO4)3 + HNO3

21. P r a c t i c e 5
Zn + HCl ZnCl2 + H2
Zn + 2HCl ZnCl2 + H2

22. P r a c t i c e 6
Al2O3 + H2O Al(OH)3
Al2O3 + 3H2O Al(OH)3

23. P r a c t i c e 7 Pb(NO3)2 + AlCl3 PbCl2 + Al(NO3)3

24. 5 types of reaction 1. Double replacement reactions (DR)
Acid base reactions are classifed as one type of
double replacement reactions
2. Single replacement reactions (SR)
3. Synthesis reactions
4. Decomposition reactions
5. Combustion reactions

25. Chemical Reactions 2Mg + O2 2MgO Types of Chemical Reactions
3. Synthesis Reaction:
Two reactants combine to give one product.
A + B AB
2Mg + O2 2MgO

26. Synthesis or combination reactions
Synthesis reactions occur when two substances (generally elements) combine and form a compound. (Sometimes these are called combination or addition reactions.)
reactant + reactant  1 product
Basically: A + B  AB
Example: 2H2 + O2  2H2O
Example: C + O2  CO2

27. Practice
Predict the products. Write and balance the following synthesis reaction equations.
Sodium metal reacts with chlorine gas
Solid Magnesium reacts with fluorine gas
Aluminum metal reacts with fluorine gas

28. Chemical Reactions Types of Chemical Reactions 4. Decomposition:
A single substance is decomposed or broken down to give two or more different substances:
AB A + B
2PbO2 2PbO + O2
2 Na HCO3 Na2CO3 + H2O + CO2

29. Decomposition Reactions
Decomposition reactions occur when a compound breaks up into the elements or in a few to simpler compounds
1 Reactant  Product + Product
In general: AB  A + B
Example: 2 H2O  2H2 + O2
Example: 2 HgO  2Hg + O2

30. Practice
Predict the products. Then, write and balance the following decomposition reaction equations:
Solid Lead (IV) oxide decomposes
Aluminum nitride decomposes

31. Chemical Reactions Types of Chemical Reactions
2. Single - Displacement Reaction:
One element reacts with a compound to take the place of one of the elements of that compound.
A + BC B + AC
Zn + 2HCl H2 + ZnCl2

32. Single Replacement Reactions
Single Replacement Reactions occur when one element replaces another in a compound.
A metal can replace a metal (+) OR a nonmetal can replace a nonmetal (-).
element + compoundelement + compound
A + BC  AC + B (if A is a metal) OR
A + BC  BA + C (if A is a nonmetal)
(remember the cation always goes first!)

33. Single Replacement Reactions
Sodium chloride solid reacts with fluorine gas
Aluminum metal reacts with aqueous copper (II) nitrate

34. Types of Chemical Reactions
1. Double - Displacement:
Two compounds exchange partners with each other to produce two different compounds.
AB + CD AD + CB
NaCl + KNO3 NaNO3 + KCl

35. More double replacement
Double Replacement Reactions occur when a metal replaces a metal in a compound and a nonmetal replaces a nonmetal in a compound
reactant + reactant  product + product
AB + CD  AD + CB

36. Double Replacement Reactions
First and last ions go together + inside ions go together
Example:
AgNO3(aq) + NaCl(s)  AgCl(s) + NaNO3(aq)
Another example:
K2SO4(aq) + Ba(NO3)2(aq)  KNO3(aq) + BaSO4(s) 2

37. 3 Driving Forces of a Double replacement reaction
Formation of a gas
Formation of a precipitate (ppt.)
Formation of a molecular compound such as water

38. Types of Chemical Reactions
5. Combustion:
A hydrocarbon reacts with oxygen to form carbon dioxide, water, and energy.
CxHy + O2 H CO2
C5H O2 H CO2

39. Combustion
Example
C5H O2  CO2 + H2O
Write the products and balance the following combustion reaction:
C10H O2  8 5 6

40. Practice
Balance and identify the type of reaction for the following equations:
Cl2 + NaBr NaCl + Br2
Ca3(PO4)2 + H2SO CaSO4 + H3PO4
C2H4 + O H20 + CO2
Na + Cl NaCl
H2O H2 + O2

41. Practice
Balance and identify the type of reaction for the following equations:
Cl2 + 2NaBr NaCl + Br2 (single replacement)
Ca3(PO4)2 + 3H2SO CaSO4 + 2H3PO4 (double displacement)
C2H O H20 + 2CO2 (combustion)
2Na + Cl NaCl (synthesis or combination)
2H2O H2 + O2 (decomposition)

42. Types of Reactions
There are five types of chemical reactions we have talked about:
Synthesis reactions
Decomposition reactions
Single displacement reactions
Double displacement reactions
Combustion reactions
You need to be able to identify the type of reaction and predict the product(s)

43. Steps to Writing Reactions
Some steps for doing reactions
Identify the type of reaction
Predict the product(s) using the type of reaction as a model
Balance it
Don’t forget about the diatomic elements! (BrINClHOF) For example, Oxygen is O2 as an element.

44. Practice Predict the products. Balance the equation
HCl(aq) + AgNO3(aq) 
CaCl2(aq) + Na3PO4(aq) 
Pb(NO3)2(aq) + BaCl2(aq) 
FeCl3(aq) + NaOH(aq) 
H2SO4(aq) + NaOH(aq) 
KOH(aq) + CuSO4(aq) 

45. Mixed Practice
State the type, predict the products, and balance the following reactions:
BaCl2 + H2SO4 
C6H12 + O2 
Zn + CuSO4 
Cs + Br2 
FeCO3 