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Reactions. Making sense of chemical equations. Types of Reactions. There are millions of reactions, and we cannot remember them all. Luckily they fall into several categories. By looking at the reactants, we will: learn the 5 major types predict the products predict if they happen at all. - PowerPoint PPT Presentation
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ReactionsMaking sense of chemical equations
Types of Reactions
• There are millions of reactions, and we cannot remember them all. Luckily they fall into several categories.• By looking at the reactants, we will:• learn the 5 major types• predict the products• predict if they happen at all
Types of Reactions
Type 1: Combination
• Combination reactions happen when 2 elements combine to make a compound (also called synthesis).
• Examples:• Ca + O2 CaO
• SO3 + H2O H2SO4
Type 2: Decomposition
• Decomposition reactions occur when a compound breaks apart into two or more elements or compounds.
• Examples:• NaCl Na + Cl2
• CaCO3 CaO + CO2
• **Note that energy is usually required.
Type 3: Single Replacement
• In a single replacement reaction, one element replaces another.• Reactants must be one element and one
compound.• Products will be a different element and a
different compound.
Type 3: Single Replacement
•Examples:
•Na + KCl K + NaCl• cation replaces cation
•F2 + LiCl LiF + Cl2
• anion replaces anion
Type 4: Double Replacement
• Double replacement reactions occur when two elements replace each other in two different compounds.• Reactants must be ionic compounds in aqueous
solution.
• NaOH + FeCl3 Fe(OH)3 + NaCl• The positive ions change places.
How to recognize each type:
•Look at the reactants:
E + E = CombinationC = DecompositionE + C = Single ReplacementC + C = Double Replacement
E = element; C = compound
Type 5: Combustion
• Combustion means “add oxygen”. • Combustion reacts occur when
compounds containing C, H, and O react with oxygen – usually called “burning”.• If the combustion reaction is complete,
the products will be CO2 and H2O.
• If the combustion reaction is incomplete, the products will be CO (possibly just C) and H2O.
Predicting Products
Type 1: Combination
•We can predict the products, especially if the reactants are two elements:•Mg + N2
• Al + Cl2
Mg3N2
AlCl3
Type 1: Combination
• Practice:• Ca + Cl2
• Fe + O2 (assume Fe (II) in the
product)
• Al + O2
Type 1: Combination
• Watch out for:• Some nonmetal oxides react with water to
form acids:• SO2 + H2O H2SO4
• **This is what happens to make “acid rain”
• Some metallic oxides react with water to for bases:• CaO + H2O Ca(OH)2
• **The hydroxide polyatomic ion indicates that the compound is a base.
Type 2: Decomposition
• We can predict the products if it is binary compound (made up of two elements) – it breaks apart into the elements.
• Examples:• H2O
• HgO
Type 2: Decomposition
• If the compound has more than two elements, you must be given at least one of the products. The other product will be made from the missing pieces.
• Examples:• NiCO3 CO2 + _______
• H2CO3(aq) CO2 + _______
Type 3: Single Replacement
• Metals will also replace other metals (and also hydrogen)• Examples:• K + AlN • Zn + HCl
• Think of water at HOH:• Metals replace the first H and then combine
with OH-. • Na + HOH
Type 3: Single Replacement
• We can even tell whether or not a single replacement reaction will happen:• Because some metals are more “active” than
others.• More active replaces less active.
• There is a list on page 217 in the textbook.• Called the Activity Series of Metals.• Higher on the list replaces lower on the list.
Type 3: Single Replacement• Rules:• 1) Metals can replace
other metals provided they are above the metal they are trying to replace. For example, zinc will replace lead.• 2) Metals above hydrogen
will replace hydrogen in acids.• 3) Metals from sodium
upward can replace hydrogen in water (HOH).
Lithium Potassium Calcium Sodium Magnesium Aluminum Zinc Chromium Iron Nickel Lead Hydrogen Bismuth Copper Mercury Silver Platinum Gold
Higher activity
Lower activity
Type 3: Single Replacement
• Practice:
• Fe + CuSO4
• Pb + KCl
• Al + HCl
Type 3: Single Replacement
• Halogens have a similar activity series. • Halogens can replace other
halogens in compounds if they are above the halogen they are trying to replace.
• Examples:• 2NaCl + F2
• MgCl2 + Br2
Fluorine Chlorine Bromine Iodine
Higher Activity
Lower Activity
Type 4: Double Replacement
• Double replacement reactions occur because of certain driving forces (or reasons). The reaction will only happen if one of the products:• doesn’t dissolve in water and forms a solid (a
precipitate), or• is a gas that bubbles out, or• is a molecular compound (which will usually
be water).
Complete and Balance
• assume all of the reactions take place
•CaCl2 + NaOH
•CuCl2 + K2S
•KOH + Fe(NO3)3
•(NH4)2SO4 + BaF2
How to recognize each type:
•Look at the reactants:
E + E = CombinationC = DecompositionE + C = Single ReplacementC + C = Double Replacement
E = element; C = compound
Practice
•H2 + O2
•H2O
•Zn + H2SO4
•HgO •KBr + Cl2
•AgNO3 + NaCl
•Mg(OH)2 + H2SO3
Type 5: Combustion
•C4H10 + O2 (assume complete)
•C4H10 + O2 (incomplete)
•C6H12O6 + O2 (complete)
•C8H8 + O2 (incomplete)
SUMMARY
• Reactions come in 5 types.• We can tell what type of reaction by looking at
the reactants.• Single replacement reactions occur based on
activity series.• Double replacement reactions occur if one
product is: 1) a precipitate, 2) a gas, or 3) water (a molecular compound).