This document discusses chemical reactions and equations. It explains that chemical reactions involve substances changing partners to form new substances, while conserving mass. Chemical equations are used to represent these reactions, showing the reactants, products, and phase changes. The document also discusses how energy is often either released or absorbed during chemical reactions, depending on whether the bonds in the products are more or less stable than the reactants. Key terms like endothermic and exothermic are introduced to describe reactions that absorb or release thermal energy.

1. Chapter 2
Section 1

3. Physical or Chemical?

4. Physical or Chemical?

5. Physical or Chemical?

6. Chemical Reaction?

7. Chemical Reaction?
A process that
produces a
chemical change

8. Chemical Equations

9. Chemical Equations
Substances that
exist before the
reaction begins

10. Chemical Equations
Substances that Substances that
exist before the form as a result
reaction begins of the reaction

11. Describe What is Happening

12. Describe What is Happening

13. Using Words
Baking Soda + Vinegar
Gas + White Solid
Charcoal + Oxygen 
Ash + Gas + Heat

14. Chemical Names
Acidic Acid + Sodium Hydrogen Carbonate 
Sodium Acetate + Water + Carbon Dioxide

15. Chemical Formula’s
CH3COOH + NaHCO3 CH3COONa + H2O + CO2
Acetic Sodium Sodium Water Carbon
Acid Hydrogen Acetate Dioxide
Carbonate

16. Arrows and Subscript

17. It’s All a Balancing Act

18. Conserve That Mass

19. Conserve That Mass
The mass of the products must be the
same as the mass of the reactants in
the chemical reaction.

20. Conserve That Mass
The mass of the products must be the
same as the mass of the reactants in
the chemical reaction.
Atoms are never lost of created in a
chemical reaction; however they do
change partners.

21. Conserve That Mass

22. Let’s Try
Tarnishing silver....
Ag + H2S  Ag2S + H2
Silver Hydrogen Silver Hydrogen
sulfide Sulfide

23. Let’s Try
Tarnishing silver....
Ag + H2S  Ag2S + H2
Silver Hydrogen Silver Hydrogen
sulfide Sulfide
• Na + AlCl3  NaCl + Al
• KBr + Cl2  KCl + Br2
• H2O2  H20 + O2

24. Energy in a Chemical Equation

25. Energy in a Chemical Equation
Energy is often released or
absorbed during a chemical
reaction.

26. Energy Released

27. Energy Released
 Where does this energy come from?

28. Energy Released
 Where does this energy come from?
 You have to think about the chemical bonds of
the reactants and the products, in order to
answer this question.

29. Energy Released
 Where does this energy come from?
 You have to think about the chemical bonds of
the reactants and the products, in order to
answer this question.
 When energy is released, the products are more
stable, and their bonds have less energy than
those of the reactants.

30. Energy Released
 Where does this energy come from?
 You have to think about the chemical bonds of
the reactants and the products, in order to
answer this question.
 When energy is released, the products are more
stable, and their bonds have less energy than
those of the reactants.
 The extra energy is released in different forms:
light, sound, thermal energy

31. Energy Absorbed

32. Energy Absorbed
 When energy is absorbed, the reactants are
more stable, and their bonds have less energy
than those of the products.

33. Energy Absorbed
 When energy is absorbed, the reactants are
more stable, and their bonds have less energy
than those of the products.
 The extra energy needed to form the products
can be supplied in the form of electricity, light,
sound, thermal energy.

34. Energy Released
2H2 + O2  2H2O + energy

35. Energy Released
2H2 + O2  2H2O + energy
2H2O + energy  2H2 + O2

36. Energy Released
2H2 + O2  2H2O + energy
Energy Absorbed
2H2O + energy  2H2 + O2

37. When thermal energy is gained or
lost, special terms are used….

38. When thermal energy is gained or
lost, special terms are used….

39. When thermal energy is gained or
lost, special terms are used….

40. When thermal energy is gained or
lost, special terms are used….
Absorb Release
thermal thermal
energy energy

41. Endothermic or Exothermic
Absorb or Release

42. Adding ENERGY to the equation

43. Finished!