Question

A flask with a volume of 1.50 L, provided with a stopcock, contains ethane gas 1C2H62 at 300 K and atmospheric pressure 11.013 * 105 Pa2. The molar mass of ethane is 30.1 g>mol. The system is warmed to a temperature of 550 K, with the stopcock open to the atmosphere. The stopcock is then closed, and the flask is cooled to its original temperature. (a) What is the final pressure of the ethane in the flask

Answer 1

Solution :

Apply ideal gas equation, PV=nRT to find the number of moles.

The number of moles of a gas is

$n=\frac{P_1V_1}{RT_1}$

$n=\frac{(11.013 \times 10^5\ Pa)(1.50 \times 10^{-3}\ m^3)}{(8.134 \ J/Mole.K)(300 \ K)}$

n = 0.66 mole

The initial mass of the ethane in the flask is

m = 0.66 mole x 30.1 g/mole

   = 19.866 g

The volume and the number of moles remains constant after the stopcock is closed.

The final pressure of the ethane is

$p_2=\frac{T_2}{T_1}p_1$

    $=\frac{300}{550} \times 11.013 \times 10^5$

  = $60.0709 \times 10^4 \ Pa$