1. Physical & Chemical Properties of Pure Substances AND Chemical Reactions

2. Properties of matter
All elements have specific physical and chemical properties
A physical property of a pure substance is anything that can be observed without changing the identity (that is, the chemical nature) of the substance.

3. Changes in Matter
A physical change does not produce a new substance (although the starting and ending materials may look very different from each other)
Changes in state or phase
(melting, freezing,
vaporization, condensation,
are physical changes).

4. Examples of Physical Changes
crushing a can
melting an ice cube
breaking a bottle
dissolving sugar into water
dissolving salt into water
crumpling a sheet of aluminum foil
casting silver in a mold

5. Changes in Matter
Chemical Changes – A change in matter that produces a new substance as the atoms rearrange themselves to form new chemical bonds
Example: The same word printed in a different order…
STAMPEDES = MADE + STEPS

6. Evidence of A Chemical Reaction
What forms of evidence show that a chemical reaction took place?
Heat is either absorbed or produced
Production of a new solid
Light is produced
Gas is produced
Change in color
Smell
Mass of object
bubbling

7. Examples of Chemical Reactions
burning a log of wood
heating popcorn
baking a cake
frying an egg
photosynthesis
moldy cheese
rusting nail
digestion of food

8. Chemical Reaction
During a chemical reaction, matter is not created or destroyed.
But what about burning a piece of wood. Burnt ash does not equal the mass of the log before it was burned?
Much of the mass is lost as carbon dioxide gas.

9. Describing Chemical Reactions
Writing Chemical Formulas
Hydrogen molecules react with Oxygen molecules to form water molecules.
--OR--
H2 + O = H2O

10. Chemical Formulas Water = H2O Carbon Dioxide = CO2 Carbon Monoxide =
Methane =
Propane =
Table Salt =
H2O
CO2 CO
CH4
C3H6
NaCl

11. Balancing Chemical Equations
3 H2O
Multiply 3 by each atom’s subscript.
3 x H2 = 6 H’s
3 x 01 = 3 0’s

12. Balancing Chemical Equations
How many atoms are present in each compound?
2 H2SO4
4 Fe2O3
6 NaCl
NO2
2 CO2H (carboxylic acid).

13. Structure of an Equation
Reactant + Reactant = Product
H O = H2O2
When a chemical reaction or change happens, the product has new and different chemical and physical properties than the reactant

14. Balancing Equations Reactants Products Element # of Atoms H O
Balance the equation
2 H2 + O2 = 2
H2O
Reactants
Products
Element
# of Atoms H O 4 4 2 2

15. Sodium NaCl
When elements chemically bond together, they make completley new substances
Let’s look at sodium chloride NaCl
Na is sodium, sodium is a silvery-white metal that is highly reactive!
At room temperature, sodium is soft enough that you can cut it with a butter knife
Cl is chlorine is a greenish-yellow, highly toxic gas

16. NaCl Continued…
But when these two elements chemically combine, they form the very common and life essential substance sodium chloride or salt!
Na Cl = NaCl
Sodium + Chlorine = Sodium Chloride

17. Types of Chemical Reactions
Synthesis
Decomposition
Replacement

18. Synthesis Reactions
When two or more substances combine to make a more complex substance.
Example: 2 H2 + O2 = 2 H2O.

19. Decomposition Reactions
The breaking down of compounds into simpler products.
Example: 2 H2O2 = 2 H2O + O2

20. Replacement Reactions
One element replaces another.
Example: 2 CuO + C = 2 Cu + CO2
Copper oxide in the presence of charcoal. The carbon of the charcoal takes the place of the copper in the copper oxide.

21. Reaction Energy Exothermic Reactions: Endothermic Reactions:
A reaction that releases energy.
Example: Car engine (combustion).
Reactants = products + energy.
Endothermic Reactions:
A reaction that absorbs energy.
Example: The formation of ice.
Reactants + energy = products