1. CHEMICAL REACTIONS
Reactants: Zn + I2
Product: Zn I2

2. Counting Atoms in a Chemical Formula
Part of a chemical formula: Aluminum oxide
2 Al2O3
Coefficient symbol subscript
Subscript- tells us how many atoms are needed to make the compound. Subscripts always come after the symbol it belongs to.
Example: 2 aluminum atoms and 3 oxygen atoms make up 1 aluminum oxide compound.
Coefficient- tells us how many molecules or formula units.
**Note**They multiply by all subscripts in the formula to get the total number of atoms.
Example: there is 2 aluminum oxide formula units (compounds)
Total atoms= 4 aluminum atoms and 6 oxygen atoms

3. Parentheses- shows that a compound has formed before it bonded with other elements to make a new compound.
The subscipts outside the parentheses multiplies by everything inside the parentheses to get the total number of atoms.
Example: Cu(NO3)2
NO3 (nitrate) formed a compound before it joined with Cu. It actually took 2 nitrates to join with 1 Cu to form this compound.
Total number of atoms = 1 copper, 2 Nitrogens, 6 oxygens.

4. Practice: Count the number of atoms of each element
H2SO4
2 H2SO4
Ba(OH)2
3 Ba(OH)2
Al2(SO4)3
2 Al2(SO4)3

5. Moles Mole is a unit used to measure amounts of a substance.
Mole – the amount of a substance that contains approximately 6.01x1023 particles of that substance.
Avogadro’s number- 6.01x1023 particles of a substance
The coeffiecients in an equation tells us how many moles of each substance.
Example: 4 Al O > 2 Al2O3
4 moles of aluminum + 3 moles of oxygen produces 2 moles of aluminum oxide.

6. Molar Mass Practice: Molar mass -The mass of one mole of a substance
You can find the molar mass of 1 atom of an element from the periodic table.
Example: 1 mole of carbon is 12 amu (on periodic table) = 12 grams (molar mass)
For a compound, you can calculate the molar mass by:
Multiply the subscripts by the mass on the periodic table
Add all elements together
expressing this sum in grams.
Practice:
H2O Molar mass = (1.0 x 2) + (15.9) = 17.9 grams
2 H2O Molar mass= (1.0 x 2) + (15.9) = 17.9 then multiply by coefficient = 35.8 grams
Ba(OH)2 Molar mass= (137.3) + (15.9 x 2) + (1.0 x 2)= 171.1g

7. Review
Chemical change –occurs when one substance changes into another substance.
You will have to know how to write a chemical formula from a name. (last chapter)
ex. Dihydrogen monoxide = H2O

8. Law of Conservation of …
Review cont.
Law of Conservation of …
Matter – Matter cannot be created nor destroyed, it can only be changed.
Energy – Energy cannot be created nor destroyed, it can only be changed.

9. Chemical Reactions Introduction
Chemical Reaction - A change in which one or more substances are converted to different substances.
Chemical reactions occur when Atoms are re-arranged as bonds are broken and formed.
Chemical reactions involve changes in matter: the making of new materials with new properties, and energy changes.
Symbols represent elements. Ex: Fe - Iron
formulas describe compounds. Ex: Fe2O3 =Iron oxide
chemical equations describe a chemical reaction
Ex: 4 Al O > 2 Al2O3

10. Chemical Reactions cont.
Nothing is lost or gained
Atoms cannot change to other atoms.
Therefore all equations must have the same number and kind of atoms on both sides of the equation.

11. Chemical Reactions
Chemical Equation- A short way to write a chemical reaction.
It shows the kind of reactants and products and their relative amounts in a reaction.
4 Al O > 2 Al2O3
3. The numbers in the front are called Coefficients. It shows how many (moles) of each substance is needed.

12. Parts of a Reaction Equation
Chemical equations show the conversion of reactants (the molecules shown on the left of the arrow) into products (the molecules shown on the right of the arrow).
A + sign separates molecules on the same side
The arrow is read as “yields”
Example
C + O2  CO2
This reads “carbon plus oxygen react to yield carbon dioxide”

13. Reactants → Product Yields forms The chemicals you start with
Produce
Yields
forms
Reactants → Product
The chemicals you start with
What you end up with after the reaction occurs

14. The charcoal used in a grill is basically carbon
The charcoal used in a grill is basically carbon. The carbon reacts with oxygen to yield carbon dioxide. The chemical equation for this reaction, C + O2  CO2, contains the same information as the English sentence but has quantitative meaning as well.

15. Signs of a Chemical Reaction
Production of a gas
Production of a precipitant
Change in color
Change in odor
Production of light or heat

16. Law of Conservation of Matter
Lavoisier, 1788
Because of the principle of the conservation of matter, an equation must be balanced.
Law of conservation of matter- matter cannot be created nor destroyed
It must have the same number of atoms of the same element on both sides.
Atoms and mass is always conserved in a chemical reaction

17. Balancing Equations
When balancing a chemical reaction you may add coefficients in front of the compounds to balance the reaction, but you may not change the subscripts.
Changing the subscripts changes the compound.
Subscripts are determined by the valence electrons (charges for ionic or sharing for covalent)

18. Subscripts vs. Coefficients
The subscripts tell you how many atoms of a particular element are in a compound. The coefficient tells you about the quantity, or number, of molecules of the compound.

19. Chemical Equations 4 Al + 3 O2 --> 2 Al2O3 This equation means
4 Al atoms + 3 O2 molecules---produces--->
2 molecules of Al2O3
AND/OR
4 moles of Al + 3 moles of O2---produces--->
2 moles of Al2O3

20. Steps to Balancing Equations
The basic steps to balancing an equation.
Write the correct formula for the reactants and the products.
Draw a line down the middle and Add up atoms on each side.
Add coefficients (one at a time), then re-add the atoms in that formula.
Compare again
Continue the trial and error process until they balance.
Reduce- If all coefficients can be reduced then reduce them to get the lowest possible whole number ratios

21. Helpful Hints Take one element at a time
working left to right except for H and O.
Save H for next to last, and O until last.
IF everything balances except for O and there is no way to balance O with a whole number
double all the coefficients and try again. (Because O is diatomic as an element)
(Shortcut) Polyatomic ions that appear on both sides of the equation should be balanced as independent units

22. Balancing equations Example
C3H8 + O CO2 + H2O
C=1
H=2
O=(2+1)=3
C=3
H=8
O=2
These are not balanced. I can only add coefficients. I can only add coefficients in the following marked spaces:
C3H8 + O CO2 + H2O
I will try to balance the “C” first by adding coefficient.

23. C3H8 + O2 3CO2 + H2O C3H8 + O2 3CO2 + 4H2O C=1 3 H=2 O=3 7 C=3 H=8 O=2
Add the coefficient and immediately re-add the letters on that side before doing anything else. **REMEMBER: Coefficients multiply by everything in the formula. +/- signs separate formulas.
C3H8 + O CO2 + H2O
C=1 3
H=2
O=3 7
C=3
H=8
O=2
My “C” is balanced but now my “H” needs to be balanced. So I know will try to balance it. It will change the “O” again.
C3H8 + O CO2 + 4H2O
C=3
H=8
O=2
C=1 3
H=2 8 O=

24. Balanced... Whoop whoop! 1C3H8 + 5O2 3CO2 + 4H2O C=1 3 C=3 H=2 8 H=8
Now the only thing that is not equal is the oxygen’s. So I will balance it.
1C3H O CO2 + 4H2O
C=1 3
H=2 8 O=
C=3
H=8
O=2 10
The Ratio = 1:5:3:4
Balanced... Whoop whoop!

26. Balancing Equations 2 3
___ Al(s) + ___ Br2(l) ---> ___ Al2Br6(s)

27. Balancing Equations 1. __C3H8 + __ O2 ---->__CO2 + __ H2O
2. __Na3PO __Fe2O >__Na2O __ FePO4
3. __B4H __O >__B2O3 + __ H2O

28. Types of Chemical Reactions

29. Synthesis reaction-
Definition: 2 or more substances combine to form another substance.
General form: A + B  AB
Example: C + O2  CO2

30. Decomposition Reactions-
Definition- when one substance breaks down, or decomposes into two or more substances.
General form: AB  A + B
Example: ZnCl2  Zn + Cl2

31. Single displacement(replacement) reaction-
Definition- when one element replaces another in a compound.
General form: A + BC  AC + B
(or) D + BC  BD + C
Example: BeF2 + Mg  MgF2 + Be

32. Double Displacement(replacement) reaction-
definition- When a precipitate, water or a gas forms when two ionic compounds in solution combine.
General form: AB + CD AD + CB
Example: HCl + KOH  KCl + H2O

33. Combustion-
Definition- a substance that reacts with oxygen producing CO2 , H2O, heat , light
General form A + O2  CO2 + H2O
Example: CH4 + 2O2  CO2 + 2H2O

34. Other Names for Reactions
Oxidation- A synthesis reaction in which a metal reacts with oxygen. Example: Iron reacting with oxygen to produce Iron oxide (rust)
Reduction- A process in which an element gains electrons during a chemical reaction. This occurs during an oxidation reaction.
Oxidation & Reduction happen together

35. Exothermic & Endothermic Reactions
Chemical reactions involve Breaking bonds and forming bonds.
Breaking bonds – require energy
Forming bonds- release energy
All chemical reactions release or absorb energy. This can be in many different forms: heat, light, sound, electricity, mechanical.
Exothermic reaction- Reaction that releases energy(feels hot). Example: combustion reactions
Endothermic reaction – absorbs energy (feels cold)

36. As you go from left to right what happens to the reactants?
They react to form products
What point on graph represents the highest energy?
At each curve’s peak
What do the double headed arrows represent?
The difference in chemical energy b/t reactants & products
Which type of reaction has products with a greater amountof energy than the reactants?
endothermic reaction

37. Reaction Rates Reaction rate- how fast a reaction occurs
Factors that affect reaction rates:
Temp- increase temp = increase rate
Surface Area- cutting an object into smaller pieces increases the surface area- increase surface area= increase rate
Stirring- increases rate
Concentration- increase concentration = increase rate
Increase pressure- increases rate
Massive, bulky molecules- react slower.

38. Catalysts
a substance that speeds up a chemical reaction without being permanently changed itself.
They are not reactants nor products.
Enzymes are proteins that are catalysts for chemical reactions in living things.

39. Inhibitors
substances that are used to combine with one of the reactants to prevent certain reactions from occurring.
ex. Food preservatives, lemon
juice on cut fruit to keep it from turning brown.