The document discusses the gas laws and how they relate to buoyancy and the behavior of gases. It introduces the gas laws of Charles, Boyle, pressure and combines them into the ideal gas law of pV=nRT. It then gives examples of using the ideal gas law to calculate volume given pressure, temperature and moles of gas. The key ideas are that gases provide buoyancy by displacing denser gases based on differences in weight, and that the gas laws can be combined into pV=nRT to relate pressure, volume, temperature and amount of gas.

1. Matter Very Simple Up, Up and Away

2. Gas Behaviour So far, we have found out: Volume is proportional to absolute temperature – Charles’ Law P ressure is proportional to absolute temperature – Pressure Law For a fixed amount of gas, the product of Pressure x Volume is constant – Boyle’s Law This may be written as P  1/V

3. The Gas Laws We will find out: Why gases provide buoyancy How all of the gas laws can be combined to give the ideal gas relationship

4. Buoyancy Things are said to be buoyant when they float… This may be a boat in water The force keeping it up is called ‘upthrust’ It is due to the weight of the displaced medium (in this case water) and is equal to weight for a floating object

5. A load of hot air! Gases can rise when in the presence of other gases. This is due to the displacement of a denser gas Helium Weight of Helium Upthrust = Weight of displaced air The resultant force is the weight of the displaced gas minus the weight of the actual gas.

6. One Law for all Gases But what happens if we combine all 4 laws..? Introducing the ‘Amount Law’…

8. Example 1 A 5 mol sample of nitrogen exerts a pressure of 150 000 Pa at a temperature of 373 K. What is the volume of this sample? Hint… pV = nRT Where p = Pressure in Pascal or Nm -2 V = Volume n = number of moles R = molar gas constant 8.31 J mol -1 K -1 T = Temperature in Kelvin Introducing Avogadro's Constant = Number of gas particles in 1 mole

10. Example 2 The temperature is changed to 273 K and the pressure drops to 100 000 Pa. What is the volume now? Hint… pV = nRT

12. The Gas Laws We will find out: Why gases provide buoyancy Resultant Force = Weight of displaced fluid – Weight of Displacing Gas How all of the gas laws can be combined to give the ideal gas relationship pV = nRT