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?

Answer 1

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