This document discusses chemical reactions and how to identify when one occurs. It defines key terms like matter, physical and chemical properties, and physical and chemical changes. It explains that a chemical reaction involves bonds breaking and forming, resulting in new substances. Signs that a chemical reaction has taken place include the formation of precipitates and changes in temperature, as reactions can be endothermic (absorb energy) or exothermic (release energy).

1. Chemical Reactions
Section 1: Observing Chemical
Change

2. Objectives
• State how matter and changes in matter can
be described.
• Explain how you can tell when a chemical
reaction occurs.

3. Key Terms
• Matter
• Chemistry
• Physical property
• Chemical property
• Physical change
• Chemical reaction
• Precipitate
• Endothermic reaction
• Exothermic reaction

4. Discovery Activity – What Happened
When Chemicals React?
• Turn to page 46 in our text book.
• What changes to you see?
• What do you notice about the temperature?
• What do you smell?

5. Observing Chemical Change
• Matter - anything that has mass and takes up
space.
• Chemistry – the study of matter and how
matter changes.

6. Properties and Changes of Matter
• Matter can be described in terms of two types
of properties
• Physical properties
• Chemical properties
• Changes in matter:
»physical changes or chemical changes

7. Properties of Matter
• Physical Properties:
– Can be observed without changing the substance
into another substance.
• Color
• Hardness
• Texture
• Shine
• Flexibility
• Ability to dissolve in water
• Ability to conduct heat

8. Properties of Matter
• Chemical Properties:
– Describes its ability to change into another
substance.
• Burning
• Tarnishing
• Rusting

9. Change of Matter
• Physical Change
– Alters the form or appearance but does not
change the substance into another substance.
• Squash a marshmallow
• Crushing
• Breaking
• Cutting
• Braiding your hair

10. Change of Matter
• Chemical Reaction
– Produces one or more new substances
• Gasoline burned in a car’s engine
• Roasting a marshmallow

11. Bonding and Chemical Change
• Chemical changes occur when bonds break
and new bonds form.
– New substances are produced.
– Magnesium + oxygen = magnesium oxide

12. Evidence for Chemical Reactions
• Chemical reactions involve two main kinds of
changes that you can observe – formation of
new substances and changes in energy.
– Precipitate: a solid that forms from solution during
a chemical reaction.

13. Changes in Energy
• Endothermic – energy is absorbed (feels
cooler)
• Exothermic – reaction that releases energy
(feels warm)