Presentation Transcript

1. Chapter 9 – Chemical Reactions
2. Changes of Matter Physical Change – a change that alters the form or appearance of a material but does not make the material into another substance: shape change, phase change, bending, tearing Chemical Change – a change that produces new substances that are made of the same elements, but change to different combinations
3. Open book to page 256-257. Read both pages. Copy the definition for Chemical Reactions What are some signs a chemical reaction has taken place?
4. Observing Chemical Reactions Chemical Reactions occur when bonds break and new bonds form Some factors that show a chemical reaction is taking place: Energy change Color change Gas formation Precipitate forming Odor Change
5. Look at Figure 2 on p. 257Which factor is happening in these situations? Soap scum forms in hard water 2. An old photograph fades in the sun 3. Bubble of methane rise off a stagnant pond 4. Your body stays warm, even in cold weather
6. Properties The chemical and physical properties of the new substances that form in a chemical reaction differ from those of the original substances. The most important sign that a chemical reaction has taken place is the formation of new substances that have new properties.
7. What evidence that a chemical reaction has occurred? 1. Baking soda and vinegar = 2. Calcium chloride and water = 3. Bromophenol Blue and Lemon Juice= 4. Alka seltzer and water =
8. + Chemical Bonds & Chemical Reactions The force that holds atoms together is called a chemical bond Chemical reactions occur when chemical bonds are either formed or broken apart 2 Hydrogen + 2 Oxygen  2 Water Molecules
9. Quick Lab: Chemical Reactions Procedure: Put the chalk (CaCO3) in the cup Add 10 mL of vinegar (C2H4O2) to the cup Look and Listen to the cup to record your observations Analysis: What evidence of a chemical reaction did you observe? What states of matter were the new substances that formed? What happened to the bonds holding the chalk together?
10. Changes in Energy Every chemical reaction involves a change in energy because energy is needed to break and form bonds Exothermic Reaction – a reaction that releases energy in the form of heat. They have an increase in temperature and would feel warm. Ex- CaCl2 and H20 Endothermic Reaction – a reaction that absorbs energy. They have a decrease in temperature and would feel cool. Ex - photosynthesis
11. Law of Conservation of Energy Energy cannot be created or destroyed but can change from one form to another Forms of energy = light, heat, electricity, chemical, kinetic, potential, nuclear
12. H2 + O2 H2O2 40g + 60g  100g Law of Conservation of Mass (or Matter) Matter is neither created or destroyed during a chemical reaction In chemical reactions, the number atoms stays the same no matter how they are arranged….so their total mass stays the same
13. What does the law of conservation of matter tell you about atoms? In your notes: Record the mass of the vinegar and baking soda Watch as the reaction takes place, record observations of the reaction What evidence of reaction took place? Record the new mass of the beaker What is the difference in mass? If the law of conservation of matter says that matter cannot be created or destroyed, then why is the new mass different than the old?
14. Homework:Page 261 #s 3-9Write the question and answer or answer in complete sentences