1. Chemical Reactions Unit 8

2. Chemical Reaction vs. Chemical Equation A REACTION is the process where 2 or more atoms or compounds rearrange themselves to form new substances. + An EQUATION is written to summarize what has happened in a reaction 2H 2 + O 2  2H 2 O

3. Signs of a Chemical Reaction 1. Precipitate formed 2. Permanent color change 3. Temperature change 4. Gas produced 5. Light produced

4. Law of Conservation of Mass Mass is neither created nor destroyed in a chemical reaction. Mass is neither created nor destroyed in a chemical reaction. Mass of the products equals the mass of the reactants in a chemical reaction Mass of the products equals the mass of the reactants in a chemical reaction Atoms only rearrange themselves Atoms only rearrange themselves

5. Practice Problems Example 1: What is the total mass of reactants in the reaction below? 2 H 2 + O 2  2 H 2 OAnswer: __________g ? 72 g Example 2: What is the total mass of products in the reaction below? AgNO 3 + NaCl  AgCl + NaNO 3 Answer: __________g 170 g 56 g---------?---------- Example 3: What is the mass of zinc produced in the reaction below? Ca + ZnCO 3  CaCO 3 + ZnAnswer: __________g 40 g 125 g 100 g ? 72 226 65

6. Chemical Equations Reactants (2H 2 (g) and O 2 (g)) Reactants (2H 2 (g) and O 2 (g)) Products (2H 2 0 (g)) Products (2H 2 0 (g)) 2H 2 (g) + O 2 (g)  2H 2 O(g) –Coefficient (The large number in front of H 2 and H 2 0) –Chemical formula –Physical state (s- solid; g- gas; aq- aqueous; l- liquid)

7. Diatomic Elements These elements are never found by themselves in nature. These elements are never found by themselves in nature. I 2, Br 2, Cl 2, F 2, O 2, N 2, H 2 I 2, Br 2, Cl 2, F 2, O 2, N 2, H 2 To help you remember, memorize this: To help you remember, memorize this: I Bring Clay For Our New Hut

8. Some other stuff you may see: Δ heat added to reactants (triangle Δ heat added to reactants (triangle  appears above arrow)  appears above arrow) Catalysts are substances that increase the rate of the reaction but are not used up themselves. The formula for the catalyst is written above the arrow: (example MnO 2 ) Catalysts are substances that increase the rate of the reaction but are not used up themselves. The formula for the catalyst is written above the arrow: (example MnO 2 )

9. Balancing Equations Copy down equation (leave space for #’s) Copy down equation (leave space for #’s) Make an atom inventory Make an atom inventory –List elements on both sides (reactants/products) –Count # of atoms on each side  Coefficient  subscript = # of atoms –Reduce if necessary! –Double check your work!

10. Types of Chemical Reactions

11. Disclaimer The events depicted in this story are fictitious. Any similarity to any person living or dead is merely coincidental.

12. The Story Begins…

13. 2H 2 + O 2 → 2 H 2 O 3Mg + N 2 → Mg 3 N 2 Synthesis Reaction A reaction in which two or more elements form a compound.

14. Synthesis Reaction + AB A B

15. The Story Continues…

16. Decomposition Reaction 2H 2 O → 2H 2 + O 2 2HgO → 2Hg + O 2 A reaction in which a compound is broken down into two or more elements.

17. Decomposition Reaction + AB B A

18. The Story Continues…

19. Single Replacement Reaction 2KCl + F 2 → 2KF + Cl 2 Mg + 2HCl → H 2 + MgCl 2 A reaction in which one element reacts with one compound to form another element and another compound.

20. Single Replacement Reaction + + AB C CB A

21. The Story Continues…

22. Double Replacement Reaction Pb(NO 3 ) 2 + K 2 CrO 4  PbCrO 4 + 2 K(NO 3 ) NaCl + AgNO 3  AgCl + Na(NO 3 ) A reaction in which the metals present in two compounds change places to form two new compounds.

23. The End! But…

24. Combustion When a carbon compound reacts with oxygen to make carbon dioxide and water. When a carbon compound reacts with oxygen to make carbon dioxide and water. –Hint:  It will always have O 2 on reactant side  It will always have CO 2 and H 2 O on product side Example: Example: CH 4 + O 2 → CO 2 + H 2 O

25. Examples 2NaCl  2Na + Cl 2 2NaCl  2Na + Cl 2 C 8 H 18 + O 2  H 2 O + CO 2 C 8 H 18 + O 2  H 2 O + CO 2 2HCl + F 2  2HF + Cl 2 2HCl + F 2  2HF + Cl 2 HCl + NaOH  HOH + NaCl HCl + NaOH  HOH + NaCl 2Na + Cl 2  2NaCl 2Na + Cl 2  2NaCl Decomposition Combustion Single Replacement Double Replacement Synthesis