Lesson 6: Chemical Reaction

• Chemical equation


  A short way of describing a chemical reaction in which symbols of the elements and the formulas of compounds represent the change

  
• Reactants are usually used up as products are formed
• Reactants yield products
• Symbols used in writing equations

  • s for solid
  • g for gas
  • l for liquid
  • aq for aqueous

  
• Catalyst


  A substance that fastens a reaction without being used up
• Catalyst is neither a reactant nor a product, so it is written above or below the arrow in the equation
• Mass cannot be created or lost through a chemical reaction so the mass of a certain element before a reaction is equal to the mass after the reaction, although the element has changed its combination
• Types of chemical reactions

  • Combination or synthesis reactions
  • Decomposition or analysis reactions
  • Single replacement reactions or substitution reactions
  • Double replacement or metabolic reactions or metathesis or ionic reactions
  • Combustion reactions

  
• Combination or synthesis reaction


  Two or more substances combine to form a single product
• Decomposition reaction


  A single compound is broken down into two or more simple substances
• Single replacement or displacement reaction


  An element replaces another element in a compound
• Single replacement reactions


  • Replacement of a metal by a more active metal
  • Replacement of hydrogen in water by a more active metal
• Decomposition processes

  • Require energy in the form of heat, light, or electricity
• Single replacement reaction


  An element replaces another element in a compound
• General equation for single replacement reaction

  • A + BC → B + AC
• Double replacement reaction


  Two compounds exchange cations to produce two different compounds
• The reaction between an acid and a base is called a neutralization reaction
• Most double replacement reactions involve ionic compounds that dissolve in water, forming homogeneous solutions
• Ions that are not directly involved in the reaction are called spectator ions
• An equation that shows only the particles that actually take part in the reaction is called a net ionic equation
• Combustion reaction


  An element or a compound reacts with oxygen, often producing energy in the form of heat and light
• All combustion reactions are exothermic
• Combustion reactions involve hydrocarbons-compounds of hydrogen and carbon
• Complete combustion of a hydrocarbon

  Produces CO₂ and H2O