Chemical Reactions Chemical Reactions UnitUnit

Learning Goal #1: Learning Goal #1: Identify evidence of Identify evidence of chemical reactions and chemical reactions and differentiate between the differentiate between the different types of different types of reactions.reactions.

Evidence for a Chemical Evidence for a Chemical ReactionReaction

PrecipitationPrecipitation– A solid formed from a solution can result A solid formed from a solution can result

from a chemical change.from a chemical change.

Evidence for a Chemical Evidence for a Chemical ReactionReaction

Gas ProductionGas Production– Fizzing, bubblingFizzing, bubbling

Color ChangesColor Changes

Odor ChangesOdor Changes

Evidence for a Chemical Evidence for a Chemical ReactionReaction

Energy ChangesEnergy Changes– ExothermicExothermic

Heat is released (feels hot)Heat is released (feels hot)

– EndothermicEndothermic Heat is absorbed (feels cold)Heat is absorbed (feels cold)

– Light can be absorbed or released also without a Light can be absorbed or released also without a temperature change.temperature change.

Predicting Whether a Reaction Predicting Whether a Reaction Will Occur Will Occur

Most common Driving Forces.Most common Driving Forces.– Formation of a solidFormation of a solid– Formation of waterFormation of water– Transfer of electronsTransfer of electrons– Formation of a gasFormation of a gas

Predicting What Will Be Predicting What Will Be Formed From a ReactionFormed From a Reaction

Solids FormsSolids Forms– PrecipitationPrecipitation

Reaction where a solid is formed.Reaction where a solid is formed.– Ionic CompoundsIonic Compounds

Contains only two types of ions.Contains only two types of ions. Anion and cationAnion and cation Strong Electrolyte: A substance that Strong Electrolyte: A substance that

dissolved in water produces ions.dissolved in water produces ions.

Steps for predicting Steps for predicting precipitatesprecipitates

Step 1 – Write the reactants as they Step 1 – Write the reactants as they actually exist before any reaction actually exist before any reaction occurs.occurs.

Step 2 – Consider the various solids Step 2 – Consider the various solids that could form.that could form.

Step 3 – Use the solubility rules to Step 3 – Use the solubility rules to decide whether a solid forms, and, if decide whether a solid forms, and, if so, to predict the identity of the solid.so, to predict the identity of the solid.

– Soluble SolidSoluble SolidSolid that readily dissolves in Solid that readily dissolves in water.water.

– Insoluble solid and slightly Insoluble solid and slightly soluble solidsoluble solidVery small amount dissolves Very small amount dissolves in water, the majority stays in water, the majority stays solid.solid.

Types of ReactionsTypes of Reactions

Decomposition ReactionsDecomposition Reactions– A compound breaks down into two or A compound breaks down into two or

more simpler substances.more simpler substances.– AB AB A + B A + B

Types of ReactionsTypes of Reactions

Synthesis ReactionsSynthesis Reactions– Two or more substances combine to Two or more substances combine to

form a single product.form a single product.– A + B A + B AB AB

Zn + I ZnI

Types of ReactionsTypes of Reactions

Single-displacement (replacement) Single-displacement (replacement) ReactionsReactions– One element takes the place of another One element takes the place of another

in a compound.in a compound.– A + BC A + BC B + AC B + AC

Acids React with Active Acids React with Active MetalsMetals

Acids react with active metals to form salts and hydrogen gas.

Mg + 2HCl MgCl2 + H2(g)

Zn + 2HCl ZnCl2 + H2(g)

Mg + H2SO4 MgSO4 + H2(g)

Double-displacement (replacement) Double-displacement (replacement) ReactionsReactions– The positive portions of two ionic The positive portions of two ionic

compounds are interchanged.compounds are interchanged.– AB + CD AB + CD CB + AD CB + AD

Types of Reactions

Acid/Base ReactionAcid/Base Reaction– Reaction between an acid and a Reaction between an acid and a

base that produces base that produces waterwater..

Types of Reactions

HCl + NaOH NaCl + H2O

H2SO4 + 2NaOH Na2SO4 + 2H2O

2HNO3 + Mg(OH)2 Mg(NO3)2 + 2H2O

Types of Reactions

CombustionCombustion– The vigorous and The vigorous and

exothermic exothermic oxidation-reduction oxidation-reduction reaction that takes reaction that takes place between place between certain substances certain substances and oxygen.and oxygen.

– Results in a flame.Results in a flame.

Methane

Oxygen

Carbon Dioxide

Water

Combustion ReactionsCombustion Reactions– One in which a substance rapidly One in which a substance rapidly

combines with oxygen to form one or combines with oxygen to form one or more oxides.more oxides.

– A + O A + O AO (oxide) AO (oxide)

Types of Reactions

Types of Reactions

Oxidation-Reduction ReactionOxidation-Reduction Reaction– A reaction that involves a transfer of A reaction that involves a transfer of

electrons.electrons.