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Chemical EquationsChemical Equations
• A shorthand way to describe a chemical reaction using chemical symbols and formulæ
Chemical EquationsChemical Equations
• Has three parts• Reactants
• Substances present before the reaction
• Products• Substances present after the reaction
• Yield Arrow• Indicates the direction of a reaction• Some reactions are reversible
Writing a Chemical EquationWriting a Chemical Equation
Chemical symbols give a “before-and-after” picture of a chemical reaction
Reactants Products
MgO + C CO + Mg
magnesium oxide to form carbon monoxide
reacts with carbon and magnesium
Balancing Chemical Balancing Chemical EquationsEquations
• Equations must be balanced to observe the Law of Conservation of Matter• Matter can not be created or destroyed
under normal reactions• If you begin a reaction with 5 g of
Hydrogen, you must end up with 5 g of Hydrogen
A Balanced Chemical EquationA Balanced Chemical Equation
Same numbers of each type of atom on each side of the equation
Al + S Al2S3 Not
Balanced
2Al + 3S Al2S3 Balanced
Balancing Chemical Balancing Chemical EquationsEquations
• Count atoms on both sides of the yield arrow
• Determine which elements are unequal• Use coefficients to balance the number
of atoms on both sides• If you multiply one element in a compound,
you multiply both elements in a compound• You can treat Polyatomic Ions as one if
they appear on both sides of the equation• Go for the highest unequal elements first• Leave solitary elements for last
Steps in Balancing An EquationSteps in Balancing An Equation
Fe3O4 + H2 Fe + H2O
Fe: Fe3O4 + H2 3 Fe + H2O
O: Fe3O4 + H2 3 Fe + 4 H2O
H: Fe3O4 + 4 H2 3 Fe + 4 H2O
Balancing Chemical Balancing Chemical EquationsEquations
Fe2O3 + C Fe + CO2
Al + FeO Fe + Al2O3
Al + H2SO4 Al2(SO4)3 + H2
Types of Chemical ReactionsTypes of Chemical Reactions
• Synthesis• Two or more substances form one new
substance
H2 + O2 H2O
N2 + H2 NH3
Types of Chemical ReactionsTypes of Chemical Reactions
• Decomposition• One substance breaks down to form two or
more new substances
PbCO3 PbO + CO2
H2CO3 H2O + CO2
Types of Chemical ReactionsTypes of Chemical Reactions
• Single Displacement• One substance replaces another in a
compound
Li + AlCl3 LiCl + Al
Types of Chemical ReactionsTypes of Chemical Reactions
• Double Displacement• Two substances “swap partners” in two
compounds
KOH + HBr KBr + H2O
NaOH + H2CO3 Na2CO3 + H2O
Types of Chemical ReactionsTypes of Chemical Reactions
• Neutralization• Double-displacement reaction where an
acid and a base form a salt and water
KOH + HBr KBr + H2O
NaOH + H2CO3 Na2CO3 + H2O
Acids and BasesAcids and Bases• Acids
• Taste Sour• Have a pH of less than 7• Produce Hydronium H3O+1 in solution• Have an “extra” H- on the beginning of the
formula
H2SO4 – (Hydro)Sulfuric Acid
H3PO4 – (Hydro)Phosphoric Acid
HNO3 – (Hydro)Nitric AcidHCl – Hydrochloric Acid
Acids and BasesAcids and Bases• Bases
• Taste bitter• Have a pH of more than 7• Produce Hydroxide OH–1 in solution• Have an –OH on the end of the formula
NaOH – Sodium Hydroxide
KOH – Potassium Hydroxide
Ca(OH)2 – Calcium Hydroxide
NH4OH – Ammonium Hydroxide
The Litmus TestThe Litmus Test
• Using an indicator can tell whether a substance is acidic or alkaline
• Litmus paper is a frequently-used indicator• Acids turn BLUE litmus paper RED• Bases turn RED litmus paper BLUE
Types of Chemical ReactionsTypes of Chemical Reactions
• Combustion• Where a carbon compound combusts with
oxygen gas to form carbon dioxide and water
CH4 + O2 CO2 + H2O
C2H6 + O2 CO2 + H2O
Let’s get it startedLet’s get it started
• Some reactions require a little “jump start” to proceed
• Activation Energy• Energy required to be applied to start a
reaction
• Examples• Applying friction to start a match• The match causing a log to burn
• Endothermic – absorbs energy from the environment to complete reaction• Feels “COLD” to its surroundings• Products have MORE energy than the
reactants
• Exothermic – releases energy to the environment as the reaction proceeds• Feels “HOT” to its surroundings• Products have LESS energy than reactants
Speeding Up
• A Catalyst is a chemical that participates in a chemical reaction without being changed by the reaction
• Catalysts speed up reaction rates by• acting as a “convenience”• lowering the activation energy
• Organic catalysts are called ENZYMES
Slowing Down
• An Inhibitor also participates in a chemical reaction without being changed by the reaction
• Inhibitors slow down reaction rates by• acting as an “inconvenience”• raising the activation energy
• Counting Atoms• Subscripts• Coefficients• Diatomic Molecules• Polyatomic Ions• Parenthesis• Oxidation Numbers• Binary Formulæ
• Criss-cross method
• Naming Rules• Ionic
• Roman Numerals
• Covalent• Prefixes
• Balancing Equations• NEVER change
subscripts• Law of Conservation
of Matter
• Types of Reactions• Changes in Energy
during reactions