Question

Liquid nitrogen trichloride is heated in a 1.75-L closed reaction vessel until it decomposed completely to gaseous elements. The resulting mixture exerts a pressure of 785 mmHg at 94°C. (a) What is the partial pressure of each gas in the container (in mmHg)? (b) What is the mass of the original sample (in g)?

Pressure of N2=?____torr Pressure of Cl2?=?_____torr

Answer 1

(a) the balanced reaction is

2 NCl₃ ............>  N₂ + 3 Cl₂

Mole fraction of N2 = 1/4

Partial pressure of N2 = mole fraction of N2 x total pressure

= (1/4) x 785 = 196 mmHg

Mole fraction of Cl2 = 3/4

Partial pressure of Cl2 = mole fraction of Cl2 x total pressure

= (3/4) x 785 = 589 mmHg

(b) Pressure P = 785mmHg = 785 /760atm

Volume V = 1.75 L

Temperature T =94 ^oC = 367 K

Ideal gas equation: PV = nRT

Total moles of N2 and Cl2 = n = PV/RT

= 785 x 1.75 /(0.082057 x 367x 760 ) = 0.0600223 mol

Moles of NCl3 = (1/2) x total moles of N2 and Cl2

= (1/2) x 0.0600223 = 0.03001113 mol

Mass of NCl3 = moles x molar mass

= 0.03001113 x 120.37 = 3.61g