Chemical Reactions

• Chemical changes are always represented by chemical equation.
• Chemical equation


  Shorthand notation that represents substances undergoing chemical reactions
• Reactants


  Substances before reaction, written on the left side of the chemical equation
• Products


  Substances resulting from the reaction, presented at the right side of the chemical equation
• Arrow symbol (→)


  Means "yields", "makes", "produces", "forms", separates the reactants from the products
• Plus sign (+)


  Indicates that the substances are added or mixed
• Down arrow (↓)


  Means that a precipitate is formed
• Up arrow (↑)


  Indicates that a gas has evolved
• Solid (s)


  Designates that the reactants or products are in solid form
• Liquid (l)


  Designates that the reactants or products are in liquid form
• A chemical reaction is usually accompanied by one or combination of the following: the production of heat and light, the formation of a precipitate, the evolution of gas, a change in color of the material or there is a change in temperature.
• Chemical reaction


  A process in which one or more substances are converted to one or more different substances
• Chemical equation


  A symbolic representation of a chemical reaction
• Chemical equation


  Symbolic representation of a chemical reaction
• Parts of a chemical equation

  • Reactants
  • Products
• Reactants


  Substances before reaction, written on the left side
• Products


  Substances resulting from the reaction, written on the right side
• Symbols used in writing chemical equations


  • +
  • →
  • ↓
  • ↑
  • (s)
  • (l)
  • (g)
  • (aq)
  • →
• Types of chemical reactions

  • Combination/Synthesis
  • Decomposition
  • Single Displacement
  • Double Displacement
  • Combustion
  • Acid-Base
• Combination/Synthesis reaction


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


  Single reactant breaks down into simpler ones
• Single Displacement reaction


  A substance replaces one of the atoms of a given compound
• Double Displacement reaction


  Ions get exchanged between two reactants, resulting in a new compound
• Combustion reaction


  Oxygen gas combines with a hydrocarbon, forming carbon dioxide and water
• Acid-Base reaction


  Acid and base react to form salt and water
• In a chemical reaction, the total mass before and after is conserved
• The number of atoms involved before and after a chemical reaction is conserved
• When sodium combines with chlorine gas

  It forms sodium chloride
• The balanced chemical equation shows the total number of atoms in the reactants is equal to the total number of atoms in the products
• Chemical equations


  They show how many atoms or molecules of a substance are involved in a reaction
• Balancing a chemical equation

  1. Write appropriate coefficients to make sure that the number of atoms on both sides of the arrow are the same

  2. Use the simplest whole number ratio
• The equation is now balanced as it has the same number of atoms on both sides
• The Law of Conservation of Mass states that the total mass of the reactants must be equal to the total mass of the products in a chemical reaction
• In balancing a chemical equation, you are allowed to write coefficients but not allowed to add new substances, change subscripts or change superscripts
• The equation 2Na + Cl2 → 2NaCl demonstrates the Law of Conservation of Mass
• Coefficients


  Numbers showing how many atoms or molecules of a given element or compound is involved in a chemical equation
• To balance the equation Na(s) + Cl2(g) → NaCl(s), the coefficients needed are 2, 1, 2
• To balance the equation NO2 → N2 + O2, the coefficients needed are 2, 1, 2