1. Chemical Reactions

2. Forming New Substances
Why do leaves change colors in the fall?
Leaves contain large amounts of chlorophyll, a green pigment, in spring and summer
During the Fall, chlorophyll breaks down into a colorless substance
the orange and yellow colors that were always present can be seen now

3. Chemical Reactions
A process in which one or more substances change to make one or more new substances
The chemical and physical properties of the new substances are different form the original substances.
Ex: leaves changing colors
mixing baking power and water makes carbon dioxide bubbles that make muffins spongy

4. Signs of Chemical Reactions
Gas formation
Solid formation- precipitate or solid is formed
Energy Change- energy is released
a fire gives off light and thermal heat
Color change

5. Chemical –vs-physical change
Physical change liquid boiling gives off a gas Chemical change liquid boiling gives off a gas and a new substance is formed with different properties from the original substance

6. Chemical Bond A force that holds two atoms together
Chemical reaction must take place to break the bonds
New bonds form
Ex: hydrogen + chlorine hydrogen chloride +

7. Writing Formulas Formulas for Covalent Bonds-
Compound composed of two non-metals
Carbon Dioxide CO2 Dinitrogen monoxide N2O
Formulas for Ionic Bonds-
Compound composed of a metal and non-metal
Sodium Chloride NaCl Magnesium chloride MgCl2

8. Prefixes used in chemical Names
mono
hexa di
Hepta
tri
Octa
tetra
nona
penta
deca

9. Chemical Equations
Uses chemical symbols and formulas as a shortcut to describe a chemical reaction
Reactants- the starting materials in a chemical reaction
Products- the substance that forms in a chemical reaction
Ex: C CO2

10. Be accurate
CO Carbon dioxide
CO Carbon monoxide
Co Cobalt

11. Balancing Equations
Atoms are never lost or gained in a chemical reaction
They are just rearranged
Every atom in the reactants becomes part of the products
The number of atoms of each element in the reactant equals the number of atoms of each element in the products

12. Ionic Compounds NaCl sodium chloride MgCl2 Magnesium Chloride
A sodium ion has a 1+ charge
A chloride ion has a 1- charge
One sodium and one chloride ion has an overall charge of 0
(1+) + (1-) = 0
A magnesium ion has a
2+ charge.
A chloride ion has a
1- charge.
One magnesium ion and two chloride ions have an overall charge of
(2+) + 2(-1)= 0

13. Formula of an ionic compound
The formula of an ionic compound is written by using enough of each ion so that the overall charge is 0.

14. Law of Conservation of Mass
Mass is neither created or destroyed in normal chemical and physical changes
The total mass of the reactants is always the same as the total mass of the products
Chemical equations must show the same number and kinds of atoms on both sides of the arrow

15. How to balance an Equation
To balance an equation you must use coefficients
Coefficient- is a number that is placed in front of a chemical symbol or formula
Ex: 2CO is 2 carbon monoxide molecules

16. Balancing an Equation
All atoms must be accounted for 1. Count all atoms 2. Multiply the subscript of each element in a formula by the formulas coefficient. Ex: 2H20 contains 4 Hydrogen atoms and 2 oxygen atoms 3. Only coefficients - not subscripts – are changed when balancing equations.

17. Balancing equations
In general, to balance an equation, here are the things we need to do:
Count the atoms of each element in the reactants and the products.
Use coefficients; place them in front of the compounds as needed.

18. Practice Na + Cl2 NaCl Mg + N2 Mg3 + N2 Na = 1 Mg= 1 Cl = 2 N= 2