©2008 Chez Chem, LLC All rights reserved. Chemical Reactions
©2008 Chez Chem, LLC Allrights reserved.
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