1. Chapter 4.3
Chemical Reactions

2. Chemical Reactions
Chemical Change – the transformation of one or more substances into different substances with different properties
Chemical Reactions
-include a change in energy energy is absorbed or releases (heat, light , sound)
-occur at different rates: some are fast others are slow

3. Chemical Equations
Represent chemical reactions by using words or symbols and formulas
Starting materials are called “reactants”
New substances are called “products”
An arrrow () is read as “produces”
States of matter appear in brackets (s)=solid (l)=liquid (g)=gas (aq) dissolved in water

4. Word Equations Use words to represent reactions
Use all of your naming rules to do this!
Ex.
Magnesium + Hydrochloric acid  Magnesium chloride + Hydrogen

5. Formula Equations Use formulas to represent reactions
Use your formula rules to do this!
Notice states of matter are always included
Coefficients are used to show the ratios of the different substances present in the reaction
Ex.
Mg (s) + 2HCl (aq)  MgCl2 (aq) + H2 (g)

6. Law of Conservation of Mass
States that in a chemical reaction, the mass of the products ALWAYS EQUALS the mass of the reactants since elements cannot be created or destroyed in a chemical reaction, they can only be rearranged!

7. Counting Atoms Rules: Just a symbol = 1 atom
Ex. N is one atom of nitrogen
Subscripts tell you the number of atoms Ex. H2 is two atoms of hydrogen
Coefficients mean to multiply everything after it by that number Ex. 2 MgCl2 means 2x1 = 2 atoms of Mg
2x2 = 4 atoms of Cl

8. Counting Atoms
4. Brackets mean to multiply everything inside by the subscript number outside the brackets
Ex. Al2(SO4)3
2= atoms Al
3x1 =3 atoms S
4X3 = 12 atoms O

9. Counting Atoms Examples
Count the atoms in the following examples
BaCl2
3 BeF2
Al (NO3)3
4 Mg3PO3

10. Homework
Counting Atoms Worksheet

11. Skeleton Equation
An unbalanced equation that shows all reactants and products in a chemical reaction written as formulas
Rules:
-write the symbol of a metal element that is NOT in a compound ex. “Iron Nail” is Fe

12. Skeleton Equations
-If the non-metal is part of Hockey stick and puck, write it as a diatomic molecule
H2, N2, O2, F2, Cl2, Br2, I2
Ex. Oxygen gas reacts with fluorine gas
O2 + F2
- Write the formula of any other compound using the rules you have learned

13. Example of Skeleton Equations
Ex. Write the skeleton equation for the reaction of sodium chloride with Magnesium phosphate to produce magnesium chloride and sodium phosphate

14. Balanced Equations
Include coefficients infront of chemical formulas to ensure that the number of each element is the same on both sides of the equation
WHY??????
You must follow the Law of Conservation of mass!

15. Balancing Rules
Balance polyatomic ions first if the same ion appears on both sides of the equation
Balance all other elements except H an O
Balance H
Balance O

16. Examples