Gas molar masses

D 3.0 moles of hydrogen gas (molar mass is 2) will have a mass of 6.0 grams. 

Notice that the density of a gas is directly proportional to its molar mass. The greater the molar mass of a gas, the more dense the gas. For this reason, a gas with a molar mass lower than that of air tends to rise in air. For example, both heUum and hydrogen gas (molar masses of 4.00 and 2.01 g/mol, respectively) have molar masses that are lower than the average molar mass of air (approximately 28.8 g/mol). Therefore, a balloon filled with either helium or hydrogen gas floats in air. 

Gas Molar Mass, gmol Density (at STP), gL- Molar Volume, L mol ... 

Gm Molar gas-phase mass flux kmol/(s-m ) (lbmol)/(h-fF)... 

The ideal gas law offers a simple approach to the experimental determination of the molar mass of a gas. Indeed, this approach can be applied to volatile liquids like acetone (Example 5.4). All you need to know is the mass of a sample confined to a container of fixed volume at a particular temperature and pressure. 

At a given temperature and pressure, die rate of effusion of a gas, in moles per unit time, is inversely proportional to the square root of its molar mass. 

In an effusion experiment, argon gas is allowed to expand through a tiny opening into an evacuated flask of volume 120 mL for 32.0 s, at which point the pressure in the flask is found to be 12.5 mm Hg. This experiment is repeated with a gas X of unknown molar mass at the same T and P. It is found that the pressure in the flask builds up to 12.5 mm Hg after 48.0 s. Calculate the molar mass of X. 

Effusion of gases. A gas with a higher molar mass (red molecules) effuses into a vacuum more slowly than a gas with a lower molar mass (gray molecules). 

Reality Check Because it takes longer for gas X to effuse, it must have a larger molar mass than argon. It does ... 

At 25°C and 380 mm Hg, the density of sulfur dioxide is 1.31 g/L. The rate of effusion of sulfur dioxide through an orifice is 4.48 mL/s. What is the density of a sample of gas that effuses through an identical orifice at the rate of 6.78 mL/s under the same conditions What is the molar mass of the gas ... 

The escape velocity required for gas molecules to overcome the earths gravity and go off to outer space is 1.12 X 103m/s at 15°C Calculate die molar mass of a species with that velocity. Would you expect to find He and H2 molecules in the earth s atmosphere How about argon atoms ... 

When iodine chloride is heated to 27°C, the weak intermolecular forces are unable to keep the molecules rigidly aligned, and the solid melts. Dipole forces are still important in the liquid state, because the polar molecules remain close to one another. Only in the gas, where the molecules are far apart, do the effects of dipole forces become negligible. Hence boiling points as well as melting points of polar compounds such as Id are somewhat higher than those of nonpolar substances of comparable molar mass. This effect is shown in Table 9.3. 

The gas phase mass transfer coefficient for the absorption of ammonia into water from a mixture of composition NHj 20%, N2 73%, Hj 7% is found experimentally to be 0.030 m/s. What would you expect the transfer coefficient to be for a mixture of composition NH3 5%, N2 60%, Hj 35% All compositions are given on a molar basis. The total pressure and temperature are die same in both cases. The transfer coefficients are based on a steady-state film model and the effective film thickness may be assumed constant. Neglect the solubility of Ny and Hi in water. 

E.12 Calculate the molar mass of the noble gas krypton in a natural sample, which is 0.3% 78Kr (molar mass 77.92 g-mol ), 2.3% 80I[Pg.69]

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