Types of Chemical Reactions Writing Chemical Reactions
Types of Reactions • Many chemical reactions have defining characteristics which allow them to be classified as to type.
Types of Chemical Reactions • The five types of chemical reactions in this unit are: • Synthesis ( Combination ) • Decomposition (includes electrolysis) • Single Replacement • Double Replacement • Combustion
Synthesis Reactions • Two or more substances combine to form one substance. • The general form is A + X AX • Example: • Magnesium + oxygen magnesium oxide • 2Mg + O2 2MgO
Combination Reactions • Combination reactions may also be called composition or synthesis reactions. • Some types of combination reactions: • Combination of elements • K + Cl2 • One product will be formed
Combination Reactions • K + Cl2 • Write the ions: K+ Cl- • Balance the charges: KCl • Balance the equation: 2K + Cl2 2KCl
Combination Reactions • Some types of combination reactions: • Oxide + water • Nonmetal oxide + water acid • SO2 + H2O H2SO3 • Metal oxide + water base • BaO + H2O Ba(OH)2
Synthesis (Combination) Reactions • Some types of combination reactions: • Metal oxides + nonmetal oxides • Na2O + CO2 Na2CO3 • CaO + SO2 CaSO3
Decomposition Reactions • One substance reacts to form two or more substances. • The general form is AX A + X • Example: • Water can be decomposed by electrolysis. • 2H2O 2H2 + O2
Decomposition Reactions • Types of Decomposition Reactions: • Decomposition of carbonates • When heated, some carbonates break down to form an oxide and carbon dioxide. • CaCO3 CaO + CO2 • H2CO3 H2O + CO2
Decomposition Reactions • Types of decomposition reactions: • Some metal hydroxides decompose into oxides and water when heated. • Ca(OH)2 CaO + H2O Note that this is the reverse of a similar combination reaction.
Decomposition Reactions • Types of decomposition reactions: • Metal chlorates decompose into chlorides and oxygen when heated. • 2KClO3 2KCl + 3O2 • Zn(ClO3)2 ZnCl2 + 3O2 • Some of these reactions are used in explosives.
Decomposition Reactions • Some substances can easily decompose: • Ammonium hydroxide is actually ammonia gas dissolved in water. • NH4OH NH3 + H2O • Some acids decompose into water and an oxide. • H2SO3 H2O + SO2
Decomposition Reactions • Some decomposition reactions are difficult to predict. • The decomposition of nitrogen triiodide, NI3, is an example of an interesting decomposition reaction.
Single Replacement Reactions • A metal will replace a metal ion in a compound. • The general form is A + BX AX + B • A nonmetal will replace a nonmetal ion in a compound. • The general form is Y + BX BY + X
Single Replacement Reactions • Examples: • Ni + AgNO3 • Nickel replaces the metallic ion Ag+. • The silver becomes free silver and the nickel becomes the nickel(II) ion. • Ni + AgNO3 Ag + Ni(NO3)2 • Balance the equation: • Ni + 2AgNO3 2Ag + Ni(NO3)
Single Replacement Reactions • Not all single replacement reactions that can be written actually happen. • The metal must be more active than the metal ion. • Aluminum is more active than iron in Al + Fe2O3 in the following reaction:
Thermite Reaction • Al + Fe2O3 • Aluminum will replace iron(III) as was seen in the video. • Iron(III) becomes Fe and aluminum metal becomes Al3+. • 2Al + Fe2O3 2Fe + Al2O3
Single Replacement Reactions • An active nonmetal can replace a less active nonmetal. • The halogen (F2, Cl2, Br2, I2) reactions are good examples. • F2 is the most active and I2 is the least. • Cl2 +2 NaI 2 NaCl + I2
Double Replacement Reactions • Ions of two compounds exchange places with each other. • The general form is AX + BY AY + BX • Metathesis is an alternate name for double replacement reactions.
Double Replacement • NaOH + CuSO4 • The Na+ and Cu2+ switch places. • Na+ combines with SO42- to form Na2SO4. • Cu2+ combines with OH- to form Cu(OH)2 • NaOH + CuSO4 Na2SO4 + Cu(OH)2 • 2NaOH + CuSO4 Na2SO4 + Cu(OH)2
Double Replacement • CuSO4 + Na2CO3 • Cu2+ combines with CO32- to form CuCO3. • Na+ combines with SO42- to form Na2SO4. • CuSO4 + Na2CO3 CuCO3 + Na2SO4
Double Replacement • Na2CO3 + HCl • Notice that gas bubbles were produced rather than a precipitate. • What was the gas? • Write the double replacement reaction first.
Double Replacement • Na2CO3 + HCl • Na+ combines with Cl- to form NaCl. • H+ combines with CO32- to form H2CO3. • Na2CO3 + 2HCl 2NaCl + H2CO3 • H2CO3 breaks up into H2O and CO2.
Double Replacement • The gas formed was carbon dioxide. • The final balanced reaction is: Na2CO3 + HCl NaCl + H2O + CO2. • Balance the equation. • Na2CO3 + 2HCl 2NaCl + H2O + CO2
Combustion Reaction • When a substance combines with oxygen, a combustion reaction results. • The combustion reaction may also be an example of an earlier type such as 2Mg + O2 2MgO. • The combustion reaction may be burning of a fuel.
Combustion Reaction • Methane, CH4, is natural gas. • When hydrocarbon compounds are burned in oxygen, the products are water and carbon dioxide. • CH4 + O2 CO2 + H2O • CH4 + 2O2 CO2 + 2H2O
Combustion Reactions • Combustion reactions involve light and heat energy released. • Natural gas, propane, gasoline, etc. are burned to produce heat energy. • Most of these organic reactions produce water and carbon dioxide.
Practice • Classify each of the following as to type: • H2 + Cl2 2HCl • Combination • Ca + 2H2O Ca(OH)2 + H2 • Single replacement
Practice • 2CO + O2 2CO2 • Combination and combustion • 2KClO3 2KCl + 3O2 • Decomposition
Practice • FeS + 2HCl FeCl2 + H2S • Double replacement • Zn + HCl ? • Single replacement • Zn + 2HCl ZnCl2 + H2
Types of Chemical Reactions • Read Chapter 8-2 • Review nomenclature • Do all of the practice exercises given in class.