1. Chemical Reactions
Chapter 11

2. Describing Chemical Change:
To understand chemical reactions we need to describe them in writing.
Reactants vs. Products
Reactants = those substances that are reacting or changing
Products = those substances that are being formed from the reactants.
Reactants Products
Yields

3. Combination (Synthesis) Reactions
Two or more substances combine to form a new compound.
A + X  AX
Must only have one product!!

4. Decomposition Reactions
A single compound undergoes a reaction that produces two or more simpler substances
AX  A + X
Must only have one reactant!!

5. Single Replacement Reactions
A + BX  AX + B
BX + Y  BY + X
Must have an element reacting with a compound
MUST use activity series… more on this next week

6. Double Replacement Reactions
The ions of two compounds exchange places in an aqueous solution to form two new compounds.
AX + BY  AY + BX
In order for this reaction to work, you must have a liquid, gas, or solid as a product. If not, it is not a reaction. More on this next week

7. Combustion Reactions The burning of natural gas, wood, gasoline
Oxygen gas must be in the reactants. Carbon dioxide and water will be in the products.
C3H8(g) + 5O2(g)  3CO2(g) + 4H2O(g)

8. Describing a Chemical Change:
Remember: All chemical reactions must follow the law of conservation of mass
What is this law?

9. Describing Chemical Change:
Skeleton Equation:
Does not indicate relative mole amounts
Shows only the formulas of the reactants and the products
Example:
Fe + O2 Fe2O3
Not Balanced!!
Can also be written as a word equation:
Iron plus oxygen yields Iron (III) oxide

10. Describing a Chemical Change
You can also indicate the state of each substance by using symbols to represent solid (s), liquid (l), gas (g) and aqueous (aq)
Example:
Fe(s) + O2 (g) Fe2O3(s)

11. Balancing Chemical Equations
Balanced equations usually contain coefficients
Coefficients = numbers placed in front of the symbol/formula for each substance
Represents the number of moles
Coefficients are always whole numbers and in the lowest whole number ratio

12. Balancing Chemical Equations:
A balanced chemical equation has the same number of atoms of each element on both sides of the equation.
Example:
2H2 + O2 2H2O
Coefficients

13. Balancing Chemical Equations:
Some helpful tips:
1. Solve the more complicated compounds first. Leave hydrogen and oxygen for the end.
2.Polyatomic ions present on both sides of the equation count as one unit.
3. When an element is present in 2 different spots on the same side, balance last.

14. Practice from worksheet
1. ___CaO ___H2O  ___Ca(OH)2
14. ___Al ___O  ___Al2O3
27. ___AgNO ___Ni  ___Ni(NO3) ___Ag
35. ___Al I ___HgCl  ____AlCl ____HgI2
48. ___CH ___O  ___CO ___H2O
49. ___C2H ___O  ___CO ___H2O