1. Types of Reactions and Balancing Equations

2.  A. also known as a “chemical change”  B. Indicators of a Chemical Reaction  1. Light production  2. Odor production  3. Heat production/Temperature Change  Exothermic - energy is released (produces heat)  Endothermic - energy is absorbed (feels cold)

3.  4. Formation of a precipitate (solid)  5. Gas production  6. Sound production  7. Color change

4.  C. Parts of a Reaction  1. REACTANTS PRODUCTS  2. Starting materials yield ending materials  3. EXAMPLE: 2 H 2 + O 2 2 H 2 O  4. Two molecules of hydrogen mixed with one molecule of oxygen yields 2 molecules of water

5.  D. Types of Equations  1. WORD EQUATIONS Reactants and products are written as words zinc + hydrochloric acid zinc chloride +hydrogen REACTANTS PRODUCTS

6.  2. FORMULA EQUATIONS  Reactants and products are written using correct formulas  These equations need BALANCED  Zn + 2 HCl ZnCl 2 + H 2

7.  E. Three Requirements for Writing Chemical Equations  1. The equation must represent the facts  2. The equation must include the symbols and formulas for all elements and compounds used or produced in the reaction  3. The Law of Conservation of Matter must be met: Atoms cannot be created or destroyed

8. SYMBOLMEANING “produces” or “yields” Indicates RESULT of reaction Indicates a reversible reaction Result is a mixture or products and reactants (s) A solid or a precipitate Na (s)

9. SYMBOLMEANING Alternative to (s), but used only to indicate a precipitate (AgCl ) (l) Liquid H 2 O (l) (aq) In aqueous solution (dissolved in water) NaCl (aq)

10. SYMBOLMEANING (g) Gas N 2 (g) A gaseous product forms CO 2 or heat Reactants are heated

11.  Step 1: Determine the reactants and products  Step 2: Write a chemical equation making sure that formulas are written correctly.  Step 3: Balance the equation. The same number of atoms of each element must be on both sides. Add coefficients to balance, NOT subscripts.

12. Subscripts coefficient PRACTICE PROBLEM #1 _____ Mg + _____ HCl _____ MgCl 2 + _____ H 2 ReactantsProducts How many Mg 1 How many Mg 1__ How many Cl 1 How many Cl __2__ How many H 1 How many H 2. Does it follow the Law of Conservation of Mass? Are there the same number of atoms of each element on both sides of the equation? NO

13. PRACTICE PROBLEM #1 _____ Mg + __2___ HCl _____ MgCl 2 + _____ H 2 ReactantsProducts How many Mg 1 How many Mg 1__ How many Cl 2 How many Cl __2__ How many H 2 How many H 2. Does it follow the Law of Conservation of Mass? Are there the same number of atoms of each element on both sides of the equation? YES!

14.  ___CuSO 4 +___ Al Al 2 (SO 4 ) 3 + ___Cu Reactants Products Cu Al SO 4

15.  1. If a polyatomic ion appears on both sides, keep it together!  2. Balance H and O last (balance those that are by themselves first)  3. Balance only by using Coefficients. NEVER change the subscripts of a formula.

16.  Zn + O 2 ZnO  HI H 2 + I 2  B + F 2 BF 3  N 2 + H 2 NH 3  Fe + H 2 O Fe 2 O 3 + H 2