1. Science 9 Unit B Section 4.0 Chemical Reactions

2. Goals For This Section 1.Identify when a chemical change occurs 2.Observe and describe evidence of chemical change 3.Distinguish between materials that readily react and those that do not 4.Observe and describe patterns of chemical change 5.Describe familiar chemical reactions and represent them with equations

3. 4.1 – Chemical Reactions  A chemical reaction takes place when two or more substances combine to form new substances  Chemical reactions involve reactants and products

4.  A chemical reaction is always written the same way, whether a word or a formula equation is used:

5. Example: Formation of Water  Word Equation:  Formula Equation:

6. Indication of Chemical Change  There are a number of observations that can indicate that chemical change has occurred:

7. Reactions & Energy  Reactions can be classified as either endothermic or exothermic  Endothermic:  Exothermic:

8. Chemical Changes Involving Oxygen  There are a number of important chemical reactions that involve oxygen as a reactant: 1. Combustion

9. 2.Corrosion 3. Cellular Respiration

10. Chemical Reaction Types  Most chemical reactions can be classified as one of five types of reactions: 1. Formation

11. 2.Decomposition 3.Single Replacement

12. 4.Double Replacement 5.Combustion

13. 4.2 – Conservation of Mass  Antoine Lavoisier carried out experiments that confirmed the Law of Conservation of Mass, which is:

14. Balanced Chemical Equations  Applying Conservation of Mass: 2 H 2 + 1 O 2 →2 H 2 O 2 mol H 2 (4g) react with 1 mol O 2 (32g) to form 2 mol H 2 O (36g)  3 H 2 + 1 N 2 → 2 NH 3 3 mol H 2 (6g) react with 1 mol N 2 (28g) to form 2 mol NH 3 (34g)  C 3 H 8 + 5 O 2 → 3 CO 2 + 4 H 2 O 1 mol C 3 H 8 (44g) react with 5 mol O 2 (160g) to form 3 mol CO 2 (132g) & 4 mol H 2 O (72g)  2 NaHCO 3 → CO 2 + H 2 O + Na 2 CO 3 2 mol NaHCO 3 (168g) decomposes to form 1 mol CO 2 (44g), 1 mol H 2 O (18g) and 1 mol Na 2 CO 3 (106g)

15. 4.3 – Factors Affecting the Rate of Reaction  Reaction rates can be changed  Some reactions may be sped up or slowed down by changing the conditions under which the reaction occurs

16. Factors Affecting Reaction Rates 1.Presence of Catalysts or Inhibitors 2.Concentration of Reactants

17. 3.Temperature of Reactants 4.The Surface Area of Reactants