Polychlorinated biphenyls (PCBs), which were formerly used in the manufacture of
ID: 909654 • Letter: P
Question
Polychlorinated biphenyls (PCBs), which were formerly used in the manufacture of electrical transformers, are environmental and health hazards. They break down very slowly in the environment. The decomposition of PCBs can be represented by the equation:
2C12H4Cl6 + 23O2 + 2H2O --> 24CO2 + 12HCL
Answer parts (a) through (e) below: a) How many moles of water are needed to react 10.0 mol O2?
b) How many grams of HCl are produced when 15.2 mol H2O react?
c) How many moles of CO2 are produced when 76.5 g HCl are produced?
d) How many grams of C12H4Cl6 are reacted when 100.25 g CO2 are produced?
e) How many grams of HCl are produced when 2.5 kg C12H4Cl6 react?
Explanation / Answer
2C12H4Cl6 + 23O2 + 2H2O --> 24CO2 + 12HCL
a) Water mol when n = 10 mol of O2 ...
ratio: 2 mol of H2O per 23 mol of O2
10 mol --> 2/23*10 = 0.869 mol of H2O
b)
15.2 mol of H2O , how many grams of HCl
ratio is 2 mol H2O : 12 mol HCl
15.2 * 12/2 = 91.2 mol of HCl will be produced
MW of HCl = 36
mass = mol*MW = 91.2*36 = 3283.2 g of HCl
c)
moles of CO2 when 76.5 g of HCl are produced
mol HCL = mass/MW = 76.5/36 = 2.13 mol of HCl
24 mol of CO2 : 12 mol of HCl
then, 2.13 mol --> 2.13*2 = 4.26 mol of CO2 will be produced
d)
if 100.25 g fo CO2 react, then we have mol = mass/MW = 100.25/44 = 2.27 mol of CO2
ratio is 2C12H4Cl6 : 24CO2
then
2.27/24*2 = 0.189 mol of C12H4Cl6
360 MW
then
mass = mol*MW = 0.189*360 = 67.6 g of C12H4Cl6
e)
if 2.5 kg react C12H4Cl6
mol = mass/MW = 2500/360 = 6.944 mol of C12H4Cl6
ratio:
2 mol of C12H4Cl6 : 12 mol of HCl
then
6*6.944 =41.6 mol of Hcl
mass = mol*MW = 41.6*36 = 1500 g of HCl or 1.5 kg