1. Ch.4 Atomic Theory Explains the formation of compounds
4.3 Chemical Equations p
Words to Know:
*balanced chemical equation *products
*chemical equation *reactants
*chemical reaction *skeleton equation
*conservation of mass *symbolic equation

2. A chemical change is the process by which one or more substances are changed into one or more new, different substances.
It has new properties
Chemical changes occur when
new substances are created.
A chemical change is the process by which one or more substances are changed into one or more new, different substances. We call this change a chemical reaction, and rarely refer to it as a chemical change.
Copper reacting in nitric acid
See pages

3. How do we know a Chemical Change has occurred?
1) Formation of a gas.
2) Formation of heat and light together.
3) Formation of a precipitate.
4) Color change.
5) Temperature change.
Color-is not a very strong indicator of a chemical reaction alone. color change but no chemical reaction (painting or coloring something, etc). 
Temp – no reaction: (warming water in a microwave, a light bulb getting hot, water freezing, etc). But, when seen with one of the three strong indicators above, it adds proof that a chemical change is occurring.

4. The original substance(s), called reactants, change into new substance(s) called products.
A + B  C
AB + CD  AC + BD
Reactants  Products

5. FeCl3 + NaOH  Fe(OH)3 + NaCl
Chemical reactions can be represented by chemical equations:
A word equation:
iron(III) chloride + sodium hydroxide  iron(III) hydroxide + sodium chloride
A symbolic equation:
FeCl NaOH  Fe(OH) NaCl

6. Both show:
reactants
products
a reaction arrow pointing from reactants to products
addition signs

7. Chemical equations may also show:
Coefficients: integers placed in front of the formula or chemical symbol
FeCl NaOH  Fe(OH) NaCl
used to determine the ratios between the various compounds in the reaction

8. States of Matter
States of matter: shown by letters written in brackets to the right of the formula or chemical symbol.
FeCl3(aq) NaOH(aq)  Fe(OH)3(s) NaCl(aq)

9. 2NO(g) + O2(g)  2NO2(g) State of matter
Letters indicate the state of each compound
(aq) =aqueous/
dissolved in water
(s) = solid
(l) = liquid
(g) = gas
Coefficients
indicate the ratio of compounds in the reaction
here, there is twice as much NO and NO2 than there is O2
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10. Conservation of Mass in Chemical Change
Chemical change means new compounds are created.
BUT no new matter is created or destroyed; atoms are just rearranged.
All matter in reactants = all matter in products
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11. Law of Conservation of Mass
In 1785 French Chemist, Antoine Lavoisier and his wife Maire-Anne stated, "We may lay it down as an incontestible axiom, that, in all the operations
of art and nature, nothing is created; an equal
quantity of matter exists both before and after
the experiment; the quality and quantity of the
elements remain precisely the same; and nothing
takes place beyond changes and modifications in the combination of these elements."

12. Law of Conservation of Mass:
Matter can not be created nor can it be destroyed
Total Mass of = Total Mass of
Reactants Products

13. Law of Conservation of Mass
John Dalton, 200 years ago, realized that atoms simply rearrange themselves during chemical reactions.
No atoms were created or destroyed.
# of atoms in reactants = # of atoms in products

14. The Law of Conservation of Mass
Mass is constant in chemical reactions,
The total mass of the products is always equal to the mass of the reactants
Mass of reactants = Mass of products
If you could collect and measure all of the exhaust from this car, you would find that mass of reactants (gas + O2) = mass of products (exhaust)!
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16. Writing and Balancing Chemical Equations
The simplest form of chemical equation is a word equation
Potassium metal + oxygen gas  potassium oxide
See page 206

17. Writing and Balancing Chemical Equations
A skeleton equation shows only the formulas of the reactants and compounds
Shows types of atoms, but not quantities
K(s) + O2 (g)  K2O(s)
A balanced chemical equation shows all atoms and their quantities
Balancing ensures that the number of each atom is the same on both sides of the reaction arrow
Always use the smallest whole number ratio
4K(s) + O2 (g)  2K2O(s)
A more useful way of representing a chemical equation is done by replacing the words with chemical symbols and formulas.
See page 206

18. Writing and Balancing Chemical Equations
A balanced chemical equation shows all types of atoms and their quantities.
Balancing ensures that the number of each atom is the same on both sides of the reaction arrow
Can only add/change coefficients to balance.
Always use the smallest whole number ratio
4K(s) + O2 (g)  2K2O(s)
Complete RC p. 207

19. Counting Atoms We count atoms in the following way:
Reactants: Na2­CO CaCl2
Na2­CO3 means 1 molecule of Na2­CO3 ( 1 x 2 Na, 1 C, and 1 x 3O)
CaCl2 means 1 molecule of CaCl2 ( 1 x Ca and 1 x 2 Cl)

20. Counting Atoms Products: CaCO3 + 2 NaCl
CaCO3 means 1 molecule of CaCO3 ( 1 x 1 Ca, 1 C, and 1 x 3O)
2 NaCl means 2 molecules of NaCl ( 2 x 1Na and 2 x 1 Cl)
Complete PP p. 207

21. Counting Atoms to Balance an Equation
Word equation: Methane + oxygen  water + carbon dioxide
Skeleton equation: CH4(g) + O2 (g)  H2O(l) + CO2(g)
To balance the compounds, take note of how many atoms of each element occur on each side of the reaction arrow.
1 Carbon, 4 Hydrogen, 2 Oxygen  1 Carbon, 2 Hydrogen, 3 Oxygen
Notes do not cover this. Students just listen
Because of the Law of Conservation of Mass, we can count atoms and use math to balance the number of atoms in chemical equations.
See page 207

22. Counting Atoms to Balance an Equation
To balance, attempt to find values that equate atoms on both sides
Balanced equation: CH4(g) + 2O2 (g)  2H2O( ) + CO2(g)
1 Carbon, 4 Hydrogen, (2x2) Oxygen 
1 Carbon, (2x2) Hydrogen, (2x1)+2 Oxygen
See page 207

23. Ex. Zinc metal and hydrochloric acid react to form zinc chloride and hydrogen gas word equation: zinc + hydrochloric acid  zinc chloride + hydrogen gas

24. Try to write the following chemical reaction as a word equation
Aluminium metal and copper(II) chloride solution react to form copper metal and aluminium chloride.

26. Copper(II) chloride solution reacts with sodium hydroxide to form copper(II) hydroxide and sodium chloride

27. Hints for Writing Word Equations
Chemical equations can be written using chemical names instead of formulas.
Eg. The chemical reaction of photosynthesis in plants consumes light energy and covnerts it into chemical energy in the form of sugar.
Word equation: carbon dioxide + water  glucose + oxygen

28. Hints for Writing Chemical Equations
Several common covalent molecules containing hydrogen have common names that do not help in writing chemical formulas
For example,
methane = CH4,
glucose = C6H12O6,
Ethane = C2H6,
Ammonia = NH3
See page 208

29. Hints for Writing Chemical Equations
The chemical symbol is used for most elements when they represent a single element. Eg Fe
Remember the formulas for the three common compounds containing hydrogen; methane CH4, ammonia NH3, and water H2O.
Be careful of polyatomic ions such as ammonium (NH4 +), and carbonate (CO3 2-).

30. Hints for Writing Chemical Equations
Be careful of diatomic and polyatomic elements
such as O2, P4 and S8
The “special seven” are all diatomic elements (hockey stick & puck)
H2, N2, O2, F2, Cl2, Br2, I2
See page 208

31. word equation:
zinc + hydrochloric acid  zinc chloride + hydrogen gas

32. Try to write the following word equation as a skeleton equation:
aluminium + copper(II) chloride solution  copper + aluminium chloride

33. copper(II) chloride + sodium hydroxide  copper(II) hydroxide + sodium chloride

34. Balancing Equations Examples
Balance the following: Fe + Br2  FeBr3
Left Right
Balance Fe:
Balance Br
X3 X2
Br =
Balance Fe again X2 X2
2 2
2 Fe + 3 Br2  2 FeBr3 S
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35. Balancing Equations Examples
Balance the following:
Sn(NO2)4 + K3PO4  KNO2 + Sn3 (PO4)4
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36. Balancing Equations Examples
Balance the following:
C2H6 + O2  CO2 + H2O
Take the Section 4.3 Quiz
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37. Strategies for Balancing Equations
Trial and error will work, but can be very inefficient
Balance compounds first, single elements last
Balance one compound at a time
Only add coefficients; NEVER change subscripts!
Balance metals first, then nonmetals, then H & O
If H and O appear in more than one place, attempt to balance them LAST
Polyatomic ions (such as SO42–) can often be balanced as a whole group
Always double-check after you think you are finished!
Complete the PP on p. 211
WB 4.3
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