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 2H2 + O22H2O

3. Signs of a Chemical Reaction • Precipitate formed • Permanent color change • Temperature change • Gas produced • Light produced

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

5. Practice Problems Example 1: What is the total mass of reactants in the reaction below? 2 H2 + O22 H2O Answer: __________g ? 72 g Example 2: What is the total mass of products in the reaction below? AgNO3 + NaCl AgCl + NaNO3 Answer: __________g 170 g 56 g ---------?---------- Example 3: What is the mass of zinc produced in the reaction below? Ca + ZnCO3 CaCO3 + Zn Answer: __________g 40 g 125 g 100 g ? 72 226 65

6. Chemical Equations 2H2(g) + O2(g)  2H2O(g) • Reactants (2H2(g) and O2(g)) • Products (2H20 (g)) • Coefficient (The large number in front of H2 and H20) • Chemical formula • Physical state(s- solid; g- gas; aq- aqueous; l- liquid)

7. Diatomic Elements • These elements are never found by themselves in nature. • I2, Br2, Cl2, F2, O2, N2, H2 • To help you remember, memorize this: IBring Clay For Our New Hut

8. Some other stuff you may see: • Δ heat added to reactants (triangle  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 MnO2)

9. Balancing Equations • Copy down equation (leave space for #’s) • 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. Synthesis Reaction A reaction in which two or more elements form a compound. 2H2 + O2 → 2 H2O 3Mg + N2→ Mg3N2

14. Synthesis Reaction + B AB A

15. The Story Continues…

16. Decomposition Reaction A reaction in which a compound is broken down into two or more elements. 2H2O → 2H2 + O2 2HgO → 2Hg + O2

17. Decomposition Reaction + AB A B

18. The Story Continues…

19. Single Replacement Reaction A reaction in which one element reacts with one compound to form another element and another compound. 2KCl + F2→ 2KF + Cl2 Mg + 2HCl → H2 + MgCl2

20. Single Replacement Reaction + + AB C CB A

21. The Story Continues…

22. Double Replacement Reaction A reaction in which the metals present in two compounds change places to form two new compounds. Pb(NO3)2 + K2CrO4 PbCrO4+ 2 K(NO3) NaCl + AgNO3 AgCl + Na(NO3)

23. The End! But…

24. Combustion • When a carbon compound reacts with oxygen to make carbon dioxide and water. • Hint: • It will always have O2 on reactant side • It will always have CO2 and H2O on product side • Example: CH4 + O2→ CO2 + H2O

25. Examples Decomposition • 2NaCl  2Na + Cl2 • C8H18 + O2 H2O + CO2 • 2HCl + F2 2HF + Cl2 • HCl + NaOH  HOH + NaCl • 2Na + Cl2 2NaCl Combustion Single Replacement Double Replacement Synthesis