1. Chapter 2.1 Observing Chemical Reactions
AISG
Glenn Jacobsen

2. Section 2.1 Observing Chemical Reactions
OBJECTIVES:
State how matter and changes in matter can be decribed.

3. Section 2.1 Observing Chemical Reactions
OBJECTIVES:
Explain how you can tell when a chemical reaction occurs.

4. Chemical Reactions are Everywhere
Cooking
Respiration

5. Chemical Reactions are Everywhere
Hair Dye
Auto Fuel

6. What is a physical property?
A characteristic of a substance that can be observed without changing the substance into another substance
Examples: ice melting, color, hardness, texture, shine, etc.

7. What is a chemical property?
A characteristic of a substance that describes its ability to change into other substances
Examples: burning magnesium, rusting

8. What is the difference between a physical and a chemical reaction?
A change in matter that produces one or more new substances is a chemical change, or chemical reaction
Physical change examples: braiding your hair, squashing a marshmallow
Chemical change examples: burning of gasoline, burning a marshmallow

9. How can you tell when a chemical reaction occurs?
Chemical changes occur when bonds break and new bonds form
Chemical reactions involve two main kinds of changes that you can observe-formation of new substances and changes in energy

10. How do you know when a chemical reaction takes place?
Color Change
Precipitate Formation

11. How do you know when a chemical reaction takes place?
Emission of light or heat

12. How do you know when a chemical reaction takes place?
Gas Formation
Odor

13. How do you know when a chemical reaction takes place?
Temperature Change
Change in Acidity

14. How do you categorize changes in energy?
Endothermic – A reaction in which energy is absorbed
Examples: baking soda and vinegar gets cooler when combined

15. How do you categorize changes in energy?
Exothermic – A reaction that releases energy in the form of heat
Examples: burning of airplane fuel

16. Is the reaction endothermic or exothermic? Explain.

17. Representing Chemical Reactions
Chemists observe chemical reactions and have come up with a way to represent or model what is happening.
Making NaCl
Solid Sodium combines with Chlorine gas to make solid Sodium Chloride:
2Na (s) + Cl2 (g)  2NaCl

18. All chemical reactions require two steps:
the atoms of the reactants are broken apart
b) the atoms of the reactants recombine to form products
e.g. magnesium + sulphuric acid ==> magnesium sulphate + hydrogen
Mg(s) + H2SO4(aq) ==> MgSO4(aq) + H2(g)