13) a) 6 mol  NH3
      b) 5 mol N2
      c) 5 mol Pb

14) a) 1 mol of N2
      b) 621 g Pb
      c) 28 g N
      d) 447 g PbO

15) (32 g O2 / 44 g CO2) x 100% = 72.7% (this is why...)

16) a) 87% of Ag2
      b) 53% of Al2
      c) 40% of Ca

17) a) 68% of Pb
      b) 10% of PbSO4

18) a & b) Reusing is when somthing is physically resued like a plastic wate rbottle being refilled or not washing your towel after every use. Recycling is when you  throw your plastic water bottle into a recycling bin and the factories turun it into the plastiv used on your plastic bags.

19) a) Renuable resources:
          - fresh water and air
          - soil
          -plants
          -animals
      b) Nonrenuable resources:
         -oil
         - cole
         - metals
         - natural gas

20) a) reusing
      b) recycling
      c) reusing

21) The life cycle of a newspaper would compare to that of a light bulb because they are both reused and recycled. The newspaper would be easier to reuse because people use newspapers as packaging with fragile products.