Chapter 6

Counting Atoms Subscripts indicate the number of atoms in a COMPOUND

Example H 2 O 2 Hydrogen Atoms 1 Oxygen The number 1 is INVISIBLE

H 2 O Coefficient Subscript

Number of Number of Molecules Atoms H2OH2O

MULTIPLY Coefficient x Subscript 2 Ag 1 Cl 2

Molecules: Two Atoms 2x1 = 2 Ag Atoms 2x2= 4 Cl Atoms 2 AgCl 2

4 NaCl Molecules = 4 Atoms: 4 Sodium Atoms 4 Chlorine Atoms

2 Ca(OH) 2 Molecules = 2 Atoms: 2 Calcium Atoms 4 Oxygen Atoms 4 Hydrogen

3 H 2 O Molecules = 3 Atoms: 6 Hydrogen Atoms 3 Oxygen Atoms

4 CO 2 Molecules = 4 Atoms: 4 Carbon Atoms 8 Oxygen Atoms

An expression that uses chemical formulas and symbols to describe a reaction

Chemical Equation R + R P + P R = Reactant P= Product

Reactants Start the reaction At the Beginning LEFT SIDE OF ARROW

“ARROW” Yields

Products New substance(s) Product = Finished RIGHT OF THE ARROW

Identify Products and Reactants

Reactants Products

Na + Cl 2 NaCl Mg + O 2 MgO

Al 2 O 3 Al + O 2 KCl + F 2 KF + Cl 2

To obey the Law of Conservation of Mass

Atoms CANNOT be created or destroyed Mass of reactants = Mass of products

Fe + S FeS 14 g + 8 g 22 g 22 g = 22 g Mass of REACTANTS Mass of PRODUCTS

Ca + Cl 2 CaCl 2 6 g + _?_ g 12 g 6 + ? g = 12 g 6 g

Fe + S FeS ? g g 44.0 g ? g = 44.0 g 28.0 g

1 Ca 2Cl 1Ca 2Cl Ca + Cl 2 CaCl 2 Balanced

Sn + Cl 2 SnCl 2 1Sn 2Cl Balanced

1Na 2F 1Na 1F Na + F 2 NaF Not Balanced 2Na + F 2 2NaF 2X1=2 2X1 =2 (Na) 2X1 = 2 (F)

Balancing Chemical Equations Step 1: Write the equation

Step 2: Count the Atoms

Step 3: Use COEFFICIENTS to Balance Atoms

H2OH2O Coefficient Subscript

Step 4: Double Check Math

_Ag + _S _Ag 2 S _Mg + _O 2 _MgO _H 2 + _N 2 _NH 3

2Ag + _S _Ag 2 S 2Mg + _O 2 2MgO 3H 2 + _N 2 2NH 3

Classifying Chemical Reactions

1. Synthesis To put together 2 reactants 1 product

Example: H 2 + O 2 H 2 O

2. Decomposition To tear apart (breakdown) 1 reactant 2 products

Example H 2 O H 2 + O 2

3. Single Replacement 2 reactants 2 products Look for a SINGLE element!

Example: Cu 2 O + C Cu + CO 2 Single Element Single Element

4. Double Replacement 2 reactants 2 products Jackpot! Compound + Compound

Example: FeS +HCl FeCl 2 + H 2 S

H2OH2O Coefficient Subscript

Number of Number of Molecules Atoms H2OH2O

MULTIPLY Coefficient x Subscript 2 Ag 1 Cl 2

Molecules: Two Atoms 2x1 = 2 Ag Atoms 2x2= 4 Cl Atoms 2 AgCl 2

4 NaCl Molecules = 4 Atoms: 4 Sodium Atoms 4 Chlorine Atoms

3 H 2 O Molecules = 3 Atoms: 6 Hydrogen Atoms 3 Oxygen Atoms

4 CO 2 Molecules = 4 Atoms: 4 Carbon Atoms 8 Oxygen Atoms

Indicators Compounds that change color when it contacts an acid or a base

Properties of Acids Sour taste Reacts with metals (corrosive) Turns litmus paper red

Properties of Bases Bitter Taste Slippery Feel Turns Litmus paper Blue

Acids Produce Hydrogen Ions (H + ) in water

Bases Produce Hydroxide ions (OH - ) in water

The pH scale

Range of numbers from 0-14 Indicates H + ions

The pH scale <7 ACID 7 Water >7 BASE