Che 026- session #5

• Physical change


  Alters the physical state of a substance without changing its composition
• Chemical change (chemical reaction)


  Converts one substance into another
• Chemical reactions


  1. Breaking bonds in the reactants (starting materials)

  2. Forming new bonds in the products
• Chemical equation


  Uses chemical formulas and other symbols showing what reactants are used as the starting materials in a reaction and what products are formed
• Writing chemical equations


  1. Reactants are written on the left

  2. Products are written on the right

  3. Coefficients show the number of molecules of a given element or compound that react or are formed

  
• The law of conservation of mass states that atoms cannot be created or destroyed in a chemical reaction
• Coefficients are used to balance an equation
• A balanced equation has the same number of atoms of each element on both sides of the equation
• Chemical equations


  • 2H2 + O2 → 2H2O
  • H2 + O2 → H2O
  • 2H2 + O2 → 2H2O
• Writing chemical equations

  1. N2 + H2 → NH3

  2. KClO3 → KCl + O2

  3. H2 + O2 → H2O

  4. CH4 + O2 → CO2 + H2O

  5. Na + H2O → NaOH + H2
• Mole


  A quantity that contains 6.02 x 10^23 items
• Avogadro's number is 6.02 x 10^23
• Relating moles to number of atoms/molecules

  1. 1 mole of C atoms = 6.02 x 10^23 C atoms

  2. 1 mole of CO2 molecules = 6.02 x 10^23 CO2 molecules

  3. 1 mole of H2O molecules = 6.02 x 10^23 H2O molecules

  
• Calculating number of molecules in moles

  • 2.5 moles of KOH
  • 4.3 moles of CS2

  
• Formula weight


  The sum of the atomic weights of all the atoms in a compound, reported in atomic mass units (amu)

  
• Calculating formula weight


  • FeCl3
  • MgOH
  • K2Cr2O7

  
• Molar mass


  The mass of one mole of any substance, reported in grams
• The value of the molar mass of a compound in grams equals the value of its formula weight in amu
• Relating grams to moles

  Molar mass can be used as a conversion factor