Effusion of gases

This equation shows that the absolute temperature is directly proportional to the average molecular kinetic energy, as postulated by the kinetic-molecular theory. Because there are N y molecules in a mole, the left-hand side of this equation is equal to the total kinetic energy of a mole of molecules. 

With this interpretation, the total molecular-kinetic energy of a mole of gas depends only on the temperature, and not on the mass of the molecules or the gas density. 

We can also obtain some useful equations for molecular speeds from the previous reasoning. Solving the equation 

We recall that m is the mass of a single molecule. So is the mass of Avogadro s number of molecules, or one mole of substance this is equal to the molecular weight, M, of the gas. 

Calculate the root-mean-square speed of H2 molecules in meters per second at 20°C. Recall that 

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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). 

The nineteenth-century Scottish chemist Thomas Graham carried out a series of experiments on the rates of effusion of gases. He found that, at constant tem-... 

Thomas Graham, a nineteenth-century Scottish chemist, did a series of experiments on the rate of effusion of gases. He found that at constant temperature, the rate of effusion of a gas is inversely proportional to the square root of its molar mass. This observation is now known as Graham s law of effusion. It follows that for two gases A and B ... 

The rates of effusion of gases are inversely proportional to the square roots of their molecular weights or densities. 

This equation is Graham s law, and thus the kinetic molecular model fits the experimental results for the effusion of gases. 

In addition to these weighing methods of determining gas gravity, a method based on the effusion of gases through a small orifice can he employed. This method is based on Graham s Law which may be stated The rate of effusion of a gas throu an orifice is inversely proportional to the square root of the gas density. Consequently, the... 

The Russians have shown that the magnitude of soil-gas values on faults increases dramatically shortly after an earthquake in which fault movement is involved (Zorkin et al., 1977). An extensive study, involving 105 observation wells, 3-5 m deep, was set up over the Mulchto oilfield in northeastern Sakhalin. A total of 3,700 samples was collected and analysed over a four-month period with the most active wells sampled daily (Table 5-IV). The results from this study provide impressive evidence for the tectonic relationship of this leakage gas flux (Fig. 5-7). This study leaves no doubt that faults and fractures provide the main control on the effusion of gases from the subsurface. 

Describe molecular motion, diffusion, and effusion of gases... 

Figure 12-14 Effusion of gases, (a) A molecular interpretation of effusion. Molecules are in constant motion occasionally they strike the opening and escape, (b) Latex balloons were filled with the same volume of He fellow), N2 (blue), and O2 (red). Lighter molecules, such as He, effuse through the tiny pores of the latex balloons more rapidly than does N2 or O2. The silver party balloon is made of a metal-coated polymer with pores that are too small to allow rapid He effusion, (c) If a bell jar full of hydrogen is brought down over a porous cup full of air, rapidly moving hydrogen diffuses into the cup faster than the oxygen and nitrogen in the air can effuse out of the cup. This causes an increase in pressure in the cup sufficient to produce bubbles in the water in the beaker.

We start with Graham s Law as this problem relates to effusion of gases. Using Graham s Law, we can calculate the effective molar mass of the mixture of CO and CO2. Once the effective molar mass of the mixture is known, we can determine the mole fraction of each component Because n a Fat constant T and P, the volume fraction = mole fraction. 

Graham also measured the effusion of gases through a small hole in a metal plate, and the transpiration of gases through capillary tubes (related to viscosity). In the first case the velocities of flow were inversely proportional to the square-roots of the densities in the second case the results were peculiar the rates of transpiration became constant with a certain length of tube and were not simply related to the densities. 

Thomas Graham determined that the rates of diffusion and effusion of gases are inversely proportional to the square roots of their molecular or atomic weights. This is Graham s Law. In general, it says that the lighter the gas, the faster it will effuse (or diffuse). Mathematically, Graham s Law looks like this ... 

Dalton s Law of Partial Pressures 12-12 Mass-Volume Relationships in Reactions Involving Gases 12-13 The Kinetic-MolecularTheory 12-14 Diffusion and Effusion of Gases 12-15 Deviations from Ideal Gas Behavior... 

The hydrogen fountain, shown in Figure 5.29, is dependent on the differences in rates of effusion of gases. (Can you explain why a heUum-filled balloon loses pressure after... 

In the mid-1800s, the Scottish chemist Thomas Graham studied the effusion and diffusion of gases. The above equation is a mathematical statement of some of Graham s discoveries. It describes the rates of effusion. It can also be used to find the molar mass of an unknown gas. Graham s law of effusion states that the rates of effusion of gases at the same temperature and pressure are inversely proportional to the square roots of their molar masses. 

During a typical day, record every instance in which you encounter the diffusion or effusion of gases (for example, when smelling perfume). 

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