Behavior of gases

1. Behavior of gases Earth Science II (Session 9)

2. Kinetic Theory • Kinetic theory proposed explainig the characteristics and properties of matter. • In essence, the theory establishes that heat and movement are related. • That the particles of all matter are in movement up to a certain point and that heat is a sign of this movement. Ciencias de la Tierra II

3. We make the following suppositions when we apply this gas theory

4. First • Gases are composed of small particules called molecules. • The distance that exists between these molecules is large compared to its size. • The total volume that the molecules occupy is a small fraction of the volume that all the gas occupies. Ciencias de la Tierra II

5. Second • There are no attraction forces (intermolecular forces) between molecules of a gas. Ciencias de la Tierra II

6. Third • The molecules are in constant rapid movement. • They colide with each other and with the walls of the container in a perfectly random way. • The frequency of the collisions with the walls explains the pressure gas has. Ciencias de la Tierra II

7. Fourth • All these molecular collisions are perfectly elastic…….. in consequence, there is no loss of kinetic energy in the system. Ciencias de la Tierra II

8. Fifth • The average kinetic energy per molecule of gas is proportional to its temperature measured in Kelvin. • The average kinetic energy of a molecule in all the gases is equal to the same temperature. Ciencias de la Tierra II

9. Kelvin is defined by two points • Absolute Zero • Triple Point of Water Ciencias de la Tierra II

10. Absolute zero is equivalent to • 273.15 oC or 0 Kelvin • Theoretically, at zero degrees Kelvin there is no molecular movement and the kinetic energy is zero. Met-Check: Weather instrumentation. (2003) Ciencias de la Tierra II

11. Triple Point Cell This illustration is adapted from C. J. Adkins, Thermal Physics The cell is cooled until ice, water, and water vapour are all present and in equilibrium. The temperature is then 273.16K by definition. A thermometer may be calibrated by inserting it into the central tube. http://eo.ucar.edu/skymath/3pt.html Ciencias de la Tierra II

12. Laws of Gases

13. Boyle’s Law • The effect of change in pressure on volume of gas at a constant temperature. V α 1 / P (Constant temperature) Boyle’s equation V1 P1 = V2 P2 Ciencias de la Tierra II

14. Application Boyle’s law • Gas has the volume of 500 ml when it is subject to a pressure of 760 mm Hg. • Calculate the volume that gas will occupy if the pressure reduces to 380 mm Hg. • Boyle’s equation is: V1 P1 = V2 P2 Ciencias de la Tierra II

15. Charles’ Law • Effect of change of temperature on the volume of gas at a constant pressure. V α T (Constant Pressure) Charles’ equation V1 / T1 = V2 / T2 Ciencias de la Tierra II

16. Application of Charles Law • Hydrogen has a volume of 1.63 liters at -10 degrees C. • Find its volume at 150 degrees Celcius supposing the the pressure is constant. • The Formula for Kelvin is: K = ºC + 273 Ciencias de la Tierra II

17. Law of combination of gases • Boyle’s law and Charles’ law can be combined to generate an equation that relates volume, temperature, and pressure of a system under different conditions: V α T V α 1 / P V α T/ P Equation of the Law of combination of Gases V1 P1/ T1 = V2 P2/ T2 Ciencias de la Tierra II

18. Application of the Combined Gas Law • Calculate the volume of oxygen in TPE conditions if the volume of gas is 450 ml when the temperature is 23 C and the pressure is 530 mm Hg. TPE = Standard conditions of temperature and pressure. The standard pressure is 0 degrees C is equivalent to 273 K and a standard pressure is1 atm or 760 mm Hg. Ciencias de la Tierra II

19. Avogadro’s Law • Effect of change on the mass of gas on the volume at a constant temperature and pressure. V α n (Constante pressure and temperature) Avogadro’s equation V1 / n1 = V2 / n2 Ciencias de la Tierra II

20. Gay-Lussac’s Law • Effect of change on the pressure of a gas at a constant volume. P α T (Constant volume) Gay-Lussac’s equation P1/ T1 = P2/ T2 Ciencias de la Tierra II

21. Law of Ideal Gas • The above laws applied together create an equation known as equation of ideal gas: PV = nRT • Where: • P = pressure • V = volume • n = moles • R = Universal Gas Constant • T = temperature Ciencias de la Tierra II

22. Application of the law of ideal Gas • What pressure does 350 g of He contain in a volume of 250 ml at a temperature of 35 C? • Atomic weight of He = 4 Ciencias de la Tierra II

23. Avogadro’s Law of molar volume • Equal volumes of different gases at the same pressure and temperature contain the same number of molecules. • Through experimentation it has been proven that the volume of 1 mol of any gas occupies a volume of 22.4 l in standard conditions of temperature and pressure, 0 ºC and 760 mm Hg. • Molar Volume = 22.4 l / mol - Ciencias de la Tierra II

24. Find the molecualr weight using molar volume • Find the molecular weight of carbon dioxide with the following data through experimentation: • Mass = 0.545 g • Volume = 297 ml • Temperature = 22 ° C • Pressure = 766 mm Hg Ciencias de la Tierra II

25. Bibliography • Chang, Raymond (1992). Química. 4ta ed. Estados Unidos de América: McGraw Hill. • Greaney, G. (2003). The horse head nebula, B33, in Orion [Imagen]. Deep sky photography. Extraído el 23 de mayo de 2003 de la World Wide Web: http://www.astroimages.com/hhead.htm • Met-Check: Weather instrumentation. (2003). Catalog [Imagen]. Met-Check: Weather instrumentation. Extraído el 23 de mayo de 2003 de la World Wide Web: http://www.metcheck.co.uk/a11.html Ciencias de la Tierra II