1. Chemical Equations and Reactions
Reactants: Zn + I2
Product: Zn I2

2. Chemical Equations and Reactions
Chemical equations show the relative amounts and types of reactants and products in a reaction.
4 Al (s) O2 (g) ---> 2 Al2O3 (s)
The numbers in the front are called
stoichiometric coefficients.
The letters after the molecule (s), (g), (aq) and (l) are the physical states of the compounds solid, gas, aqueous and liquid.

3. Chemical Equations and Reactions
Elements are pure substances that cannot be broken down into other substances. Theses are represented by chemical symbols.
Examples are: Ca, Br, H, C, Mg
Compounds are homogeneous substances made up of two or more elements chemically combined.
Examples are: NaCl, KBr, F2, H2O

4. 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 equation reads “carbon plus oxygen react to yield carbon dioxide”

5. Balancing Equations Rules
When balancing a chemical reaction you may place 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).

6. 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.

7. Reading Chemical Equations
Equations can be read in terms of atoms and molecules or moles, so…
The equation
4 Al(s) O2(g) ---> 2 Al2O3(s)
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

8. Steps to Balancing Equations
There are four basic steps to balancing a chemical equation.
Write the correct formula for the reactants and the products.
Find the number of atoms for each element on the left side. Compare those against the number of the atoms of the same element on the right side.
Determine where to place coefficients in front of formulas so that the left side has the same number of atoms as the right side for EACH element in order to balance the equation.
Check your answer to see if:
The numbers of atoms on both sides of the equation are now balanced.
The coefficients are in the lowest possible whole number ratios. (reduced)

9. Example

10. Reaction Types There are 5 basic reaction types Synthesis
Decomposition
Single Replacement
Double Replacement
Combustion

11. 1. Synthesis Reactions
Synthesis reactions occur when two substances (generally elements) combine and form a compound.
Reactant A + Reactant B 1 Product AB
Basically: A + B  AB
Examples: 2H2 + O2  2H2O
C + O2  CO2 2Mg + O2  2 MgO

12. Synthesis Reaction Example

13. 2. Decomposition Reactions
Decomposition reactions occur when a compound is broken down into two or more simpler substances.
1 Reactant AB  Product A + Product B
In general: AB  A + B
Example: 2 H2O  2H2 + O2
2 HgO  2Hg + O2
2 Al2O3  4 Al + 3 O2

14. Decomposition Reaction Example

15. 3. Single Replacement Reactions
Single Replacement Reactions occur when one element replaces another in a compound.
A + BC  BA + C
Example: Zn + H2SO4  ZnSO4 + H2

16. Single Replacement Example

17. 4. Double Replacement Reactions
Double Replacement Reactions occur when a metal replaces a metal in a compound and a nonmetal replaces a nonmetal in a compound
Compound + Compound  Product + Product
AB + CD  AD + CB
Example:
NaCl + AgNO3  NaNO3 + AgCl

18. Double Replacement Reactions
Think about it like “foil”ing in algebra, 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)  2KNO3(aq) + BaSO4(s)

19. 5. Combustion Reactions
Combustion reactions occur when a hydrocarbon reacts with oxygen gas.
CxHy + O2  CO2 + H2O
Products in combustion are ALWAYS carbon dioxide and water.
Example:
CH4 (g) + 2O2(g)  CO2(g) + 2H2O(g)