SCE

• Chemical reaction


  A process in which one or more substances are converted to one or more different substances
• Chemical changes are always represented by a chemical equation
• Chemical equation


  A symbolic representation of a chemical reaction

  
• Parts of a chemical equation

  • Reactants
  • Products
• Reactants are the substances before reaction and written on the left side of the chemical equation
• Products are the substances resulting from the reaction and presented at the right side of the chemical equation
• Reactants and products are separated by an arrow (→)
• Symbols used in writing chemical equations


  • + (indicates that the substances are added or mixed)
  • → (means "yields", "makes", "produces", "forms" and separates the reactants from the products)
  • ↓ (means that a precipitate is formed)
  • ↑ (indicates that a gas has evolved)
  • (s) (designates that the reactants or products are in solid form)
  • (l) (designates that the reactants or products are in liquid form)

  
• Chemical reactions are 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 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 reacts 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


  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 is applied to get the same number of atoms of every element on each side of the equation
• Things you are allowed to do when balancing a chemical equation

  • Add new substance
  • Change subscripts
  • Change superscripts
  • Write coefficients