Question

1) Dichlorine monoxide is a powerful oxidizing agent that is used to bleach wood pulp and to treat municipal water supplies. It is made by the reaction

SO2(g) + 2Cl2(g) SOCl2(g) + Cl2O(g)

If you put SO2 in a flask so that its pressure is 125 mm Hg at 22°C, and if you add Cl2 gas to this same flask, what should the Cl2 partial pressure be in order to have the correct stoichiometric ratio of SO2 to Cl2?

2) Continuing Question 1 above… if you react 0.235 g SO2 with a stoichiometric amount of Cl2, what is the total pressure of the reaction products in a 250. mL flask at a temperature of 85°C after both reactants have been used up?

Answer 1

Stoichiometric ratio of SO₂ and Cl₂ is 1:2

mole of SO₂ = 1

moles of Cl₂ = 2

mole fraction of SO₂ = 1/(1+2) = 1/3

mole fraction of Cl₂ = 2/(1+2) = 2/3

now, partial pressure of SO₂ = Total pressure * mole fraction of SO₂

or, 125 = P_total * 1/3

or, P_total = 375 mm Hg

again, partial pressure of Cl₂ = Total pressure * mole fraction of Cl₂

or, partial pressure of Cl₂ = 375 *2 /3 = 250 mm Hg.

.

2.

moles of SO₂ taken = 0.235/64 = 0.0037 [molar mass of SO₂ = 64 g/mol]

then, moles of Cl₂ should be required = 2*0.0037 = 0.0074

1 mole SO₂ and 2 mole Cl₂ reacts completely to form 1 mole SOCl₂ (g)  and 1 mole Cl₂O (g)

now, when 0.0037 mole SO₂ and 0.0074 Cl₂ completely reacts , 0.0037 moles SOCl₂ (g)  and 0.0037 moles Cl₂O (g) is formed.

hence , total mole of the gaseous products = 0.0037+0.0037 =0.0074

now using , Ideal gas equation

PV = nRT

given

Volume (v) = 250 ml = 0.25 L

Temperature ( T) = 85⁰c = 358 K

R = 0.082 L-atm /mol.K

and calculate moles (n) = 0.0074

then, total pressure (P) = nRT/V

= 0.0074*0.082*358/0.25 = 0.869 atm = 660.39 mm Hg.