1. Chapter 6.2 Describing Chemical ReactionsBy
Mrs. Totten

2. What are Chemical Equations?
Short, easy way to show a chemical reaction using symbols instead of words.
Example
Hydrogen reacts with oxygen to yield water

3. Structure of an Equation
Tells you the substances you start with and the substances you get at the end.
REACTANTS – substances you have at the start
PRODUCTS – substances you get at the end of the reaction

4. In a chemical reaction, matter is not created or destroyed !
Conservation of Mass
In a chemical reaction, matter is not created or destroyed !
the number of atoms you start with must equal the number of atoms you end with
Total mass of reactants must equal total mass of the products.

5. Conservation of Mass:
5ml
5ml
10ml

6. Open System – chemical reaction
matter can enter from or escape to the surroundings
Burning : Oxygen enters reaction and CO2, ash and heat escape

7. Closed System – chemical reaction
Matter is not allowed to enter or leave
Molding bread in zip-lock baggie

8. Balancing Chemical Equations
Equation is balanced when it shows CONSERVATION OF MASS
There must be same number of each type of atom on both sides of equation
Example:
N O NO2

9. Balancing Equations

10. Coefficients
Number placed in front of a chemical formula in an equation
Tells you how many atoms or molecules of a reactant or a product take part in a reaction
If coefficient is 1 you don’t write it!
Example: 4H2O + 2O H + 4O2

11. Balancing Equations:
H O H2O