Question #156989

A) A 1.00 g gaseous sample of hydrocarbon occupies a volume of 385 mL at 330 K and 1.00 atm. Find the molar mass of the compound.

B) Calculate the number of atoms of He(g) that are needed to exert a pressure of 4.0 X 10â€“2Â kPa in a 15 mL container at a temperature of â€“23Â°C.

Expert's answer

A) A 1.00 g gaseous sample of hydrocarbon occupies a volume of 385 mL at 330 K and 1.00 atm. The molar mass of the compound is found using gas law:

p*V=m/M*RT

M = m*RT/(p*V) = 1 g * 8.31 J/(K*mole)*330 K / (385*10^{-6} m^{3} * 101325 Pa) = 70.30 g/mole

B) The number (N) of atoms of He(g) that are needed to exert a pressure of 4.0 X 10â€“2Â kPa in a 15 mL container at a temperature of â€“23Â°C is found using gas law:

p*V = N*k*T

N = p*V/(k*T) = 40 Pa * 15*10^{-6} m^{3} / (1.38*10^{-23} J/K * 350 K) = 1.27*10^{17}

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