Quarter 4: Physical Science

• Indications of a Chemical Reaction

  • Evolution of heat, light, and sound
  • Production of new gas or vapor
  • Formation of a precipitate
  • Input or release of energy
  • Change in color and odor
  • Difficult to reverse
• Chemical Equations


  Depict the kind of reactants and products and their relative amounts in a reaction
• Stoichiometric Coefficients


  Numbers in front or before the reactants and products
• Phases in Chemical Equations


  • Solid phase
  • Liquid phase
  • Gas phase
• Solid phase


  (s), substance is relatively rigid and has a definite volume and shape
• Liquid phase


  (l), substance has a definite volume, but is able to change the shape by flowing
• Gas phase


  (g), substance has no definite volume or shape, and it shows little response to gravity
• The Law of Conservation of Matter/Mass: 


  the same atoms are present in a reaction at the beginning (reactants) and at the end (products), the amount of matter in a system does not change
• The Law of Conservation of Matter/Mass:


  atoms are neither created or destroyed
• Chemical Equations must be balanced because of the principle of the conservation of matter
• Chemical Equations must have the same number of atoms of the same kind on both sides
• Characteristics of Chemical Equations


  • Must present known facts
  • Must contain the correct formulas for the reactants and products
  • Must satisfy the law of conservation of matter/mass
• Reactants


  The substances that exist before a chemical change (reaction) takes place
• Products


  The new substances that are formed during the chemical change
• Word Equations


  Describes the chemical change using the names of the reactants and products
• Balanced Chemical Equations


  Number of atoms of each element as a reactant is equal to the number of atoms of that element as a product
• Conservation of mass and the fact that a balanced equation will always have the same number of atoms of each element on both sides of an equation


  When substances react and form new substances, no atoms are created or destroyed. They just rearrange to form new combinations. When balancing a chemical equation we are basically making sure that there will be the same number of each type of atom on both sides of the equation. So, balancing the equation keeps everything fair and obeys the rule that mass is always conserved.
• How to balance a chemical reaction?


  1. Write a word equation for the reaction

  2. Write the correct formulas for all reactants and products

  3. Determine the coefficients that make the equation balance
• Coefficient


  • The number before each reactant or product
  • A 'multiplier' for every atom in the molecule
• Subscript


  Refers to the number of atoms of this type that are present in each molecules
• Guidelines for Balancing Chemical Equations


  • Polyatomic ions (groups of two or more ions) first
  • All number of atoms must be even
  • Single elements last
• Symbol: →


  'Yields'; indicates result of reaction
• Symbol: ⇌


  Used to indicate a reversible reaction
• Symbol: (s)


  A reactant or product in the solid state; also used to indicate a precipitate
• Symbol: (l)


  A reactant or product in the liquid state
• Symbol: (aq)


  A reactant or product in an aqueous solution (dissolved in water)
• Symbol: (g)


  A reactant or product in the gaseous state
• Symbol: Δ →


  Reactants are heated
• Symbol: 2 atm →

  Pressure at which reaction is carried out
• Symbol: pressure →


  Pressure at which reaction is carried out exceeds normal atmospheric pressure
• Symbol: 0°C →


  Temperature at which reaction is carried out
• Symbol: Pt →


  Formula of catalyst used to alter the rate of the reaction
• Combustion Reactions


  Occurs when oxygen reacts with a hydrocarbon to produce water and carbon dioxide
• Combustion Reaction


  • C10H8 (s) +12O2 (g) -> 10CO2 (g) + 4H2O (g)
• Hydrocarbon


  A compound containing only carbon, hydrogen, and sometimes oxygen
• Synthesis or Combination


  The combination of 2 or more substances to form a compound; only one product
• Synthesis or Combination


  • 2 CU+O2 -> 2CuO
• Decomposition


  A compound breaks down into 2 or more simpler substances; only one reactant
• Decomposition


  • 2CuO -> 2 CU+O2
• Single Replacement


  Occurs when a single element reacts with an ionic compound and switches places with one of the elements in the compound