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Reaction Types

Reaction Types. Section 5.2. Objectives. Distinguish among five general types of chemical reactions Predict the products of some reactions based on the reaction type Describe reactions that transfer or share electrons between molecules, ions, or atoms. But why?.

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Reaction Types

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  1. Reaction Types Section 5.2

  2. Objectives • Distinguish among five general types of chemical reactions • Predict the products of some reactions based on the reaction type • Describe reactions that transfer or share electrons between molecules, ions, or atoms

  3. But why? • Scientists are lazy. Classifying reactions allows us to make predictions about what will happen in a reaction without thinking about it too hard. • Good news for you: Knowing the reaction type will help you make decisions on a test regarding the outcomes of such equations.

  4. The 5 Reaction Types • Synthesis • Decomposition • Combustion • Single-displacement • Double-displacement

  5. Synthesis Reactions • Definition: Reaction of at least two substances that forms a new, more complex compound • General Reaction format: • A + B  AB • Example: • Na + Cl2  NaCl (not balanced) • 2Na + Cl2  2NaCl (balanced!)

  6. More about Synthesis Reactions • Synthesis  Synthesize  Make something new • What kind of reaction is “Photosynthesis?” • What does photosynthesis synthesize? • 6CO2 + 6 H2O  C6H12O6 + 6O2

  7. Decomposition Reactions • Definition: A reaction in which one compound breaks into at least two products • General Reaction format: • AB  A + B • Example: • H2O  H2 + O2 (not balanced) • 2H2O  2H2 + O2 (balanced!)

  8. More about Decomposition Reactions • Decomposition  decompose  break something down • How do synthesis and decomposition compare? • Electrolysis (using an electric current) is a type of decomposition reaction.

  9. Combustion Reactions • Definition: A reaction in which a compound and oxygen burn • General Reaction format: • A + oxygen  stuff (usually water, CO2) • Example: • CH4 + O2  CO2 + H2O (not balanced) • 2CH4 + 4O2  2CO2 + 4H2O (balanced!)

  10. More about Combustion Reactions • Combustion  combust  burn or explode • Can synthesis and combustion reactions be alike? • Think about hydrogen and oxygen reacting together • As oxygen in a combustion reaction is reduced, the products contain more carbon monoxide, then finally solid carbon (soot).

  11. Single-displacement Reactions • Definition: A reaction in which atoms of one element take the place of atoms of another element in a compound • General Reaction format: • XA + B  BA + X • Example: • CuCl2 + Al  AlCl3 + Cu (not balanced) • 3CuCl2 + 2Al  2AlCl3 + 3Cu (balanced!)

  12. More about Single-displacement reactions • A locked-up atom is released while a free atom is locked-up. (false arrest?) • Potassium and water exhibit a single-displacement reaction K + H2O  KOH + H2 • How about the Thermite reaction? • Iron oxide + Aluminum  Aluminum oxide + iron

  13. Double-displacement Reactions • Definition: A reaction in which a gas, a solid precipitate, or a molecular compound is formed from the apparent exchange of ions between two compounds • prisoner exchange? • General Reaction format: • AX + BY  AY + BX • Example: • Pb(NO3)2 + K2CrO4  PbCrO4 + 2KNO3

  14. Loose ends • Reduction-oxidation (redox) reaction: A reaction that occurs when electrons are transferred from one reactant to another (useful in batteries) • Radicals: Fragments of molecules that have at least one electron available for bonding (useful for making polymers like Styrofoam)

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