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Types of Chemical Reactions

Learn about synthesis, decomposition, single displacement, and double displacement reactions, as well as energy exchange and reaction mechanisms. Includes common symbols used in chemical equations.

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Types of Chemical Reactions

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  1. Chapter 21 Types of Reactions

  2. Synthesis • Two or more substances combine to form a more complex substance • General Form: reactant + reactant  product • A + B  AB

  3. Synthesis • Combination of an acidic oxide with water will result in an acid • Acids usually start with a hydrogen Ex: SO2 + H2O  H2SO3 • Combination of the metal of a basic oxide with the nonmetal of an acidic oxide will form a salt Ex: CO2 + Na2O  NaCO3

  4. Synthesis • Combination of a basic oxide or a metallic oxide with water to form a base. • Most bases end with a hydroxide ion (OH) Ex: Na2O + H2O  2NaOH

  5. A compound breaks down into two or more simpler substances The reaction is started when electricity, light, or heat is supplied The opposite of synthesis reactions General Form: reactant  product + product AB  A + B Decomposition

  6. Decomposition • If some of the acids are heated, they decompose to form water and an acidic oxide. Ex: H2SO3 SO2 + H2O • When some metallic hydroxides are heated, they decompose to form a metallic oxide and water.Ex: Ca(OH)2 CaO + H2O

  7. Decomposition • Some metallic carbonates decompose to form a metallic oxide and carbon dioxide when heated.Ex: Li2CO3 Li2O + CO2 • Metallic chlorates decompose to form metallic chlorides and oxygen when heated.Ex: KClO3 2KCl + 3O2

  8. Decomposition • Most metallic oxides are stable, but a few decompose when heated.Ex: 2HgO  2Hg + O2 • Some compounds can not be decomposed by heat, but can be decomposed into their elements by electricity. (=electrolysis)ex: 2H2O = 2H2 + O2

  9. Single Displacement • A single uncombined element replaces another in a compound • General Form: element + compound  element + compound • A + BX  AX + B

  10. Single Displacement • An active metal will displace the metallic ion in a compound of a less active metal. Ex: Fe + Cu(NO3)2 Fe ( NO3)2 + Cu • Some active metals will react with water to give a metallic hydroxide & hydrogen gas.Ex:2Na + 2H2O  2NaOH + H2

  11. Single Displacement • Active metals such as zinc, iron & aluminum will displace the hydrogen in acids to give a salt & hydrogen gas. Ex: Ex: Zn + 2HCl  ZnCl2 + H2 • Halogens (which are active nonmetals) will displace less active halogens. Ex: Cl2 + 2NaBr  2NaCl + Br2

  12. Double Displacement • Parts of two compounds switch places to form two new compounds • The positive and negative ions of two compounds are interchanged. • General Form: compound + compound  compound + compound • Ax + By  Ay + Bx

  13. Double Displacement • A reaction between an acid and a base yields a salt and water. Such a reaction is a neutralization reaction.Ex: 2KOH + H2SO4 K2SO4 + 2H2O • Reaction of some soluble salts produces an insoluble salt and a soluble salt.Ex: AgNO3 + NaCl  AgCl + NaNO3 Na2SO4 + Ba(NO3)2 BaSO4 + 2NaNO3

  14. Double Displacement • Reaction of a salt with an acid forms a salt of the acid and a second acid which is volatile.Ex: 2KNO3 + H2SO4 K2SO4 + 2HNO3 FeS + 2HCl  FeCl2 + H2S • This same reaction of a salt with an acid or base may yield a compound which can be decomposed.Ex: CaCo3 + 2HCl  CaCl2 + H2CO3 H2C03 CO2 + H2O

  15. Energy Exchange in Reactions • Chemical reactions involve energy exchange • Breaking chemical bonds requires energy. • Forming chemical bonds releases energy. • Exothermic reactions- reaction where energy is given off in the form of heat • Ex: burning of wood, iron rusting • Endothermic reactions- reaction that absorbs energy from its surroundings (decomposition rxn) • Ex: salt dissolving in water

  16. Reaction Mechanisms • Reaction Mechanism– an outside substance that is added to a reaction to affect the rate of production • Catalyst – speeds up a chemical reaction without itself being permanently changed • Mass of the product formed is still the same, it just forms more rapidly • Inhibitor – prevents or slows a chemical reaction or interferes with a catalyst’s action • Ex: food preservatives in cereal and crackers

  17. Common Symbols 1. (s) – solid2. (l) – liquid3. (g) – gas4. (aq) – aqueous (indicates that the chemical is in a water solution)5. (ppt) – precipitate (solids that are insoluble in water & settle to the bottom of a solution.) *many double displacement reactions produce precipitates

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