1. Chemical Reactions Balancing Reactions

2. Rxn vs Equation Chemical reaction is a process where the atoms of 2 or more elements or compounds rearrange to form new substances. Chemical Equation summarizes the details of a particular chemical reaction.

3. Signs of a chemical reaction Change in color Formation of a gas (odor) Light/ Heat produced Change in temperature –(absorbs/releases energy) Formation of precipitate

4. Law of Conservation of Mass mass is neither created nor destroyed in a chemical reaction total mass stays the same atoms can only rearrange

5. Example 1: What is the total mass of reactants in the reaction below? 2 H2 + O2  2 H2OAnswer: __________g ? 72 g Example 2: What is the total mass of products in the reaction below? AgNO3 + NaCl  AgCl + NaNO3Answer: __________g 170 g 56 g---------?---------- Example 3: What is the mass of zinc produced in the reaction below? Ca + ZnCO3  CaCO3 + ZnAnswer: __________g 40 g 125 g 100 g ? 72 226 65

6. Chemical Equations Reactants Products 2H 2 (g) + O 2 (g)  2H 2 O(g) –Coefficient –Chemical formula –Physical state (s, solid; g, gas; aq, aqueous; l, liquid) Diatomic elements. H 2 N 2 O 2 F 2 Cl 2 Br 2 I 2

7. 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 MnO 2 )

8. 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 √

9. Chemical Reactions Types of Reactions

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

11. The Story Begins…

12. 2 H 2 + O 2 → 2 H 2 O 3 Mg + N 2 → Mg 3 N 2 Synthesis Reaction A reaction in which two or more elements form a compound.

13. The Story Continues…

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

15. The Story Continues…

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

17. The Story Continues…

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

19. The End! But…

20. Combustion 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: CH 4 + O 2 → CO 2 + H 2 O

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