Properties and composition of air. Gas Laws

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Properties and composition of air: The first properties were observed in the gases were transparency, the ability of compression and expansion and diffusion capacity.
The air pressure: The first property of the air was a quantitative study of the pressure, whose measure is essential to establish the laws of gases.
Chemical composition of air: The Earth's atmosphere is a mixture of gases. Four of these constitute 99 percent of total volume x, so often referred to as major components of the air. This is because Lagran variability of its presence in the air. The concentration of most atmospheric gases subjected to variations, seasonal and altitude.

Ideal gas laws

Boyle's Law

The compressibility of air is a proven fact. In a glass tube J-shaped, closed at one end and poured a quantity of mercury, so that at the closed end was trapped air volume. Adding successive amounts of mercury, I can get more compressed air. After each portion of mercury measured aggregate volume of trapped air and the pressure at which this was sometido.PV = constant Boyle could not control the temperature at which conducted their experiment, but assuming that remained constant. At constant temperature, pressure and volume of a fixed amount of gas are inversely proportional.

Law of Charles and Gay Lussac

After the work of Boyle, was made a sustained effort to discover the effect of temperature changes on the pressure and volume of a gas. Boyle repeating the experiment at different temperatures are obtained different curves is called isotherms. The existence of these curves is an indication that the temperature influences the pressure for the same volume, or volume for the same pressure. If the pressure remains constant, the volume increases with increasing temperature, ie, the gas expands. The relationship between volume and temperature was determined by Charles. " In a sealed tube at one end, put a small amount of mercury, which enclose a given mass of air in the closed end of the tube. As the temperature increases observed that the mercury amounted cap, increasing the volume of trapped air. The results of the experiment can be represented in a diagram volume temperature, obtaining a line that intersects the x-axis in the first quadrant. If the line is extended to negative temperatures, cuts the axis at -273 ° C. V / T = constant

For a fixed amount of gas kept at constant pressure, volume and absolute temperature are directly proportional. This law was established by Gay Lussac in 1808 and confirmed by Dalton. The laws of Boyle and Charles can be combined into an equation that relates pressure, volume and temperature for a fixed mass of gas. Suppose a mass of gas enclosed in a balloon that we go through three consecutive states characterized by the values of volume, temperature, and pressure. This law is very useful to know the volume of a gas under conditions of P and T determined, knowing the volume occupied by the same gas under different conditions of P and T different.

Avogadro's Hypothesis

Avogadro's hypothesis set out in 1811 says that equal volumes of all gases, measured under the same conditions of pressure and temperature contain the same number of molecules. The scale sought to measure the amount of gas is the number of molecules, which is enough to incorporate the concept of mole. If the combined law replace the constant term by the number of moles of gas, we obtain the general equation of ideal gases. PV = nRT In this equation r is the ideal gas constant whose value depends on the units in which they measured the pressure and volume. When the volume is measured in liters, the pressure in atmospheres and the temperature in kelvin: R = 0.082 atm.litro / mol / deg.

Dalton's law of partial pressures

Often the relationship is needed between PV and T of a mixture of gases. This requires understanding how this relates the total pressure of the mixture with the individual components. Each gas exerts a pressure within the mixture, which is called partial pressure. In 1801 Dalton formulated a law, known as the law of partial pressures Dalton, which states that the total pressure of a mixture of gases is the sum of the pressures that each gas would exert if it were alone.

Graham's law of diffusion

In a container in which there is a gas, we introduce a second gas, after a while the two gases form a homogeneous mixture. The two gases mix in gradually to form a mixture is a phenomenon known as diffusion and was studied by Thomas Graham in 1832 by establishing a law that says that under the same pressure and temperature conditions, the rates of gaseous diffusion are two inversely proportional to the square root of the molar masses. This law is known as the law of diffusion of Graham. This equation is used to describe the phenomenon of the effusion. to di

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