# Behaviour of gases

Thermal diffusion If a temperature difference is applied to a uniform mixture of two gases, the mixture will partially separate into its components, with the heavier, larger molecules usually but not invariably concentrating at the lower temperature. This method, called equimolar countercurrent diffusion, is the usual manner in which gaseous diffusion measurements are now carried out. The ideal gas law is easily extended to mixtures by letting n represent the total number of moles of all species present in volume V. The first to do the latter was Graham in ; he kept the pressure uniform by allowing the gas mixture to flow. It also depends on the geometry of the tube, but this effect will not be considered here.

The transport coefficient describing the diffusion thermoeffect must be equal to the coefficient describing thermal diffusion, according to the reciprocal relations central to the thermodynamics of irreversible processes. Light molecules have higher average speeds than do heavy molecules at the same temperature.

Find the increase in pressure if the gas is heated to 0C. Although the average kinetic energy of the liquid is below the boiling point, some molecules have above average energy. This behaviour was predicted theoretically before it was observed experimentally, but a rather elaborate explanation was required because simple theory suggests no such phenomenon.

The interpretation of the temperature dependence of E is particularly simple for dilute gases, as is shown in the discussion of the kinetic theory of gases below. This phenomenon was also observed by Graham in A system with many kinds of motion on a molecular scale absorbs more energy than one with only a few kinds of motion. If the diffusion takes place in a closed vessel, the pressure difference drives the heavy gas into the light-gas region at Behaviour of gases faster rate than it would otherwise diffuse, and a steady state is quickly reached in which the number of heavy molecules traveling in one direction equals, on the average, the number of light molecules traveling in the opposite direction.

Equilibrium behaviour is much easier to analyze, because any change that occurs on the molecular level must be compensated by some other change or changes on the molecular level in order for the system to remain in equilibrium.

By measuring the quantity of gas in moles rather than grams, the constant R is made universal; if mass were measured in grams and hence v in volume per gramthen R would have a different value for each gas.

Can you guess the vapor pressure of water at degrees Celsius. The steady-state pressure difference that develops is almost unmeasurably small unless the diffusion occurs through a fine capillary or a fine-grained porous material.

Robert Boyle noted this peculiar phenomenon inbut his results were largely either ignored or forgotten. Finally, there is no obvious correlation of gas viscosity with molecular weight.

A given mass of gas has a volume of ml at 25 0C. The ideal gas concept is useful because it obeys the ideal gas law, a simplified equation of state, and is amenable to analysis under statistical mechanics. In most usual conditions (for instance at standard temperature and pressure), most real gases behave qualitatively like an ideal gas.

CHAPTER 12, The Behavior of Gases(continued) The fourth variable is the amount of gas in the system. the ideal gas law true the combined gas law Boyle’s law The combined gas law allows calculations for situations where none of the variables—pressure, temperature, or volume—are constant.

The Theories and Behavior of Gas. Updated on February 21, Liwayway Memije-Cruz. more. why the behaviour of gases is different from other materials?

Jeriemae DelaCruz. It is very informative article of what is the theories and behavior of gases is. A gases is one of the three forms of matter. Gases: Properties and Behaviour Gas Laws Partial Pressures Kinetic Theory and Ideal Gases Real Gases Diffusion and Effusion.

Learning objectives Describe properties of gases and define ideal gas Describe the physical basis for pressure Identify units of pressure and convert between. Gas - Behaviour and properties: The enormous number of molecules in even a small volume of a dilute gas produces not complication, as might be expected, but rather simplification.

The reason is that ordinarily only statistical averages are observed in the study of the behaviour and properties of gases, and statistical methods are quite accurate when large numbers are involved.

Gas particles move in random, straight-line motion. Gas particles possess a greater kinetic energy than the particles of a liquid or solid. The greater kinetic energy is due to gases existing at higher temperatures than liquids or solids.

Behaviour of gases
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