1. Chemical Change
Chapter 3
Section 3.1

2. Objectives Identify important reactions in society
Recognize and identify evidence for chemical changes
Differentiate between endothermic and exothermic reactions
Describe the Law of Conservation of Mass

3. To Start
What is the difference between a chemical and physical change?
Chemical change- something new is created with its own unique properties
Physical change- nothing new is created (just changing states)
What are the three states?

4. Chemical or Physical?
Which of the following are chemical changes? Physical changes?

5. Chemical Change Reactant + reactant  product(s)
Products have different properties than reactants
Properties include: state at RT, temperature, melting point, color and density
Includes a flow of energy
IMPORTANT: drives chemical reactions
Can be fast or slow

6. Examples of Chemical Reactions
Batteries
Combustion Engine
Wine production
Baking bread
Photosynthesis
Cellular respiration (making energy in our bodies)

7. Evidence of a Chemical Change
What are ways that we know a chemical change has occurred?
Formation of a gas (bubbles)
Air bag inflation in a car
Color change
Sugar and sulfuric acid
Formation of a precipitate (change in state)
Mixing silver nitrate with sodium chloride
Flow of energy (usually detected as a change in temperature)
Combustion (lighting a match)

8. Formation of a Gas: Demo
What will happen when I add baking soda to vinegar in this beaker?
What will happen to the balloon placed over the top?
What gas is produced?
What other examples do we have of a formation of a gas?

9. Energy Changes Two types of energy changes:
Exothermic- release of energy (*exit)
Endothermic- absorption of energy (*enter)
What change of temperature would you feel with each of these processes?
Can physical changes be exothermic and endothermic? Why or why not?

10. Exothermic Reactions Release energy, usually as:
heat (flame)
light (bioluminescence)
Electricity (battery)
Important ex.: Combustion
What is combustion?
Combustion- oxygen reacts rapidly with another substance, releasing energy (burning)
2C6H14(l) + O2(g)  12CO2(g) + 14H2O(g) + energy
(Combustion of hexane)

11. Endothermic Reactions
Absorb energy
Ex. Cold packs- squeeze package, breaks pack inside which keeps chemicals separate; absorb energy and whole mixture cools down
Ex. Photosynthesis
Energy + 6CO2(g) + 6H2O(l)  C6H12O6(aq) + 6O2(g)

12. Biochemical Reactions
They may be endothermic or exothermic
They are almost always helped by enzymes (biological catalysts)
Catalysts are chemicals that speed up a reaction but are not used up by it.
Photosynthesis and Cellular Respiration

13. Law of Conservation of Mass
Developed by Antoine Lavoisier
Total mass of the reactants equals the total mass of the products
Using this, we can deduce that:
** total # of atoms present before a reaction equals the total # of atoms after a reaction

14. Example
If I get 13 g of H2O and 15 g of NaCl from the reaction of HCl and NaOH, how much NaOH did I use, if I used 10 g of HCl?
HCl(aq) + NaOH(aq)  H2O(l) + NaCl(aq)
10g ? g g
Answer: 18 g