Question

A) a 14.0 g sample of N2 gas occupies what volume at 0 °C?
B) which gas is most dense at 2 atm and 400 K? F2, N2, Ne, or O2?
C) Which gas has the greatest average molecular speed at 298 K? CH4, CO2, N2, or Xe?
D) what volume of oxygen gas, measured at 27°C and 0.987 atm is produced from the decomposition of 67.5g of HgO?

Answer 1

Given: 14g N2  

the key is volume and STP
volume of any gas at STP is 22.4 L (at 273 K)

14 g N2 x (1.0 mol N2 / 28 g N2) x ( 22.4 L N2 / 1 mol N2)
= 11.2 L N2

B)

PV = (mass / mw) RT
(mass / V) = mw x P / (RT)

and since density = mass / V...
density = mw x P/(RT)

therefore, at the same P and T, the gas with the HIGHEST mw will have the highest density.

mw O2 = 32 g/mole
mw N2 = 28 g/mole
mw Ne = 20.17 g/mole
mw f2 = 38 g/mole

so F2 has highest density

C)

the molecular speed is inversely proportional to the mass of the gas.

CH4= 16 g

CO2= 44 g

N2=28 g

Xe=131 g

So the gas with highest molecular speed is CH4.

D)

decomposition of HgO:

2HgO ----> 2Hg + O2

67.5 g HgO =>

no. of moles= 67.5/217 = 0.311

2 moles of HgO produces 1 mole of O2

0.311 moles produces= 0.1555 moles of O2

PV=nRT

V= nRT/P

R= 0.082

V= 3.875 L