1. Chemical Reactions:
Chp 8

2. Describing Chemical Change:
To understand chemical reactions we need to describe them in writing.

3. Describing a Chemical Change:
Chemical reaction = one or more substances change into one or more new substances

4. Describing Chemical Change:
Reactants vs. Products
Reactants = those substances that are reacting or changing
Products = those substances that are being formed from the reactants

5. Describing Chemical Change:
In writing a chemical reaction, an arrow is used to separate the reactants from the products
The arrow ( ) = yields, gives or reacts to produce

6. Describing Chemical Change
Remember: All chemical reactions must follow the law of conservation of matter
What is this law?

7. Describing Chemical Change:
Chemical equations: using chemical formulas to describe in writing a chemical reaction
The arrow separates the formulas of the reactants from the formulas of the products

8. Describing Chemical Change:
Skeleton equation:
Does not indicate relative amounts
Shows just the formulas of the reactants and products
Example:
Fe O Fe2O3

9. Describing Chemical Change:
You can 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)

10. Describing Chemical Change:
Catalyst ?
A substance that speeds up the rate of a reaction but is not used up in the reaction

11. Balancing Chemical Equations:
If there is no indication of the quantity of reactants and products in a equation, it is unbalanced

12. Balancing Chemical Equations:
Balanced equations usually contain coefficients:
Coefficients = numbers placed in front of the symbols for the respective parts

13. Balancing Chemical Equations:
Balanced chemical equation = has the same number of atoms of each elements on each side of the equation

14. Balancing Chemical Equations:
Example:
C(s) O2(g) CO2(g)
Each side of the equation has the same number of carbon and oxygen atoms
The equation is balanced

15. Balancing Chemical Equations:
Rules: page 208

16. Balancing Chemical Equations:
Additional rules:
1. Solve the more complicated compounds first
2. Any polyatomic ions present on each side of the equation count as one unit
3. Solve the single elements last