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Chemical Reactions

•Reactants – the substancesthat exist before a chemicalchange (or reaction) takes place.

•Products – the newsubstance(s) that are formedduring the chemical changes.

•CHEMICAL EQUATION indicates thereactants and products of a reaction.

REACTANTS PRODUCTS

Common Symbols

• yields, produced

• (aq) aqueous solution (dissolved in water)

• (g) gas or

• (l) liquid

• (s) or (cr) or for a precipitate

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Types of Reactions

Single displacement

Double displacement

Synthesis

Decomposition

There are 4 basic types of reactions

Single Displacement• A + BC B + AC

OR

• A + BC C + BA

• Either the metal or non metal is replaced• Metal replaces metal OR non metal replaces non metal

• Compound + element

• Examples: Na + HOH NaOH + H2

• OR Cl2 + NaBr Br2 + NaCl

Double Replacement

• AB + CD AD + CB

• Elements do the dosie doe

• Compound + compound

• They change partners

• Also called a METATHESIS

• Precipitation reactions - later

Example: sodium iodide reacts with magnesium nitrate

Double-replacement reaction

CaCO3 + 2 HCl CaCl2 + H2CO3

General form:

AB + CD AD + CB

Single-replacement reaction

Mg + CuSO4 MgSO4 + Cu

General form:

A + BC AC + B

Synthesis

• A + B AB

• Element + element yields a compound• Example: hydrogen + oxygen produces water

Decompositions

• Metal hydroxide

• Metal carbonate

• Metal chlorate

• Oxy acid

• Metal oxide

• ba = base anhydride• aa = acid anhydride

Decompositions

• Metal hydroxide ba + water

• Metal carbonate ba + CO2

• Metal chlorate metal chloride + O2

• Oxy acid aa + water• Metal oxide metal + O2

• ba = base anhydride• aa = acid anhydride

Oxy acids

• This is the one where you MUSTdetermine the oxidation numberof the non metal in the acid inorder to get the correct aa

• Example:• H3PO4 H20 + P2O5

Combustion• Combustion of Hydrocarbons:

• Another important type of reaction, in addition tothe four types above, is that of the combustion of ahydrocarbon. For us, when a hydrocarbon is burnedwith sufficient oxygen supply, the products arealways carbon dioxide and water vapor. If,however, the supply of oxygen is low or restricted,then carbon monoxide will be produced. This is whyit is so dangerous to have an automobile enginerunning inside a closed garage or to use a charcoalgrill indoors.

• Hydrocarbon (CxHy)  +  O2(g)  →    CO2(g)  +  H2O(g)

• EX. CH4+  2O2  →    CO2(g)  +  2H2O(g)

Now atoms must be balanced

• According to the law ofconservation of mass theremust be the same number ofeach atom on BOTH sides of theequation

• Every chemical compound has aformula which cannot bealtered.

Do not change formulas• You can ONLY change the

coefficients when thecompounds are writtencorrectly

• 2H2 + O2 2H2O

• 2 + 2

Balancing Equations

• First write the correct formulas forreactants and products.

• Balance polyatomic ions as units.

• Make sure there are the samenumber of each atom on both sidesof the equation.

• NEVER change subscripts informulas ONLY coefficients.

Predicting Products

• Recognize the type of reaction.

• Memorize the basic types ofdecompositions.

• Know your polyatomic ions.

• Review basic nomenclature.

Precipitation Reactions

• All reactions occur in aqueoussolutions.

• All reactions are doubledisplacements – dosie doe

• Must use the Table ofSolubilities to determine theNET IONIC EQUATION and thespectator ions.

Formation of a solid: Silver chloride

AgNO3(aq) + KCl(aq) KNO3 (aq) + AgCl(s)

Table of SolubilitiesMAINLY WATER

SOLUBLE

• NITRATES• All nitrates are soluble

• ACETATES• All acetates are soluble

• CHLORATES• All chlorates are soluble

• CHLORIDES• All chlorides are soluble except

Hg2+2, Ag+, and Pb+2 (HAP)

• BROMIDES• All bromides are soluble except

Hg+2, Hg+1, Ag+1, and Pb+2 (HAP)

• IODIDES• All iodides are soluble except

Hg+2, Hg+1, Ag+1, and Pb+2 (HAP)

• SULFATES• All sulfates are soluble except

Ca+2, Ba+2 Sr+2 (CBS), Hg+2, Hg+1,Ag+1, and Pb+2 (HAP)

MAINLY WATERINSOLUBLE

• SULFIDES• All sulfides are insoluble except those of IA

and 2A elements and ammonium

• CARBONATE• All carbonates are insoluble except those of

1A elements, Mg+2 and ammonium

• SULFITE• All sulfites are insoluble except those of IA

elements and ammonium

• PHOSPHATE• All phosphates are insoluble except those of IA

elements and ammonium

• HYDROXIDE• Hydroxides are insoluble except Ca+2, Ba+2 Sr+2

(CBS), are moderately soluble and elements ofIA and ammonium are soluble. The oxides andhydroxides of all other metals are insoluble.

• CHROMATE• All chromates are insoluble except those of IA

elements and ammonium

• DICHROMATE• All dichromates are insoluble except those of

IA elements and ammonium

Facts about solubility• INSOLUBLE

• does not dissolve, i.e., forms a precipitate

• SOLUBLE• does dissolve, i.e., does not form a precipitate

• *MODERATELY SOLUBLE• dissolves only slightly, i.e., forms a precipitate at

specific concentrations - considered insoluble

• *NOTE The following are the "date-lessdudes": nitrate, chlorate, acetate,ammonium, lithium, sodium, and potassium

AgNO3(aq) + KCl(aq) KNO3 (aq) + AgCl(s)

Write in ionic form

Ag+1 (aq) + NO3-1

(aq) + K+1 (aq) + Cl-1 (aq) AgCl + K+1 (aq) + NO3

-1 (aq)

Net ionic: Ag+1 (aq) + Cl-1 (aq) AgCl

Spectator ions: K+ , NO3-

The processWrite balanced equations from

words

Predict products

Write net ionic equations

Example:

Sodium sulfate reacts with barium chloride in aqueous solution

Write in ionic form

2Na+1(aq)+ SO4

-2 (aq)+ Ba+2 (aq)+ 2Cl-1

(aq) BaSO4 + 2Na+1(aq)+ 2Cl-1

(aq)

Net ionic: Ba+2 (aq) + SO4-2 (aq) BaSO4

Spectator ions: Na+1 , Cl-1