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Gases

Gases. Volume, Pressure & Temperature. Volume: Total space occupied by a substance The volume of a gas can either increase (expansion) or decrease (contraction) Volume of a gas increases when the number of moles of gas increases Volume of a gas increases when temperature increases

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Gases

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  1. Gases

  2. Volume, Pressure & Temperature Volume: Total space occupied by a substance • The volume of a gas can either increase (expansion) or decrease (contraction) • Volume of a gas increaseswhen the number of moles of gasincreases • Volume of a gas increases when temperatureincreases • Volume of a gas increases when pressuredecreases

  3. Volume, Pressure & Temperature Volume: Total space occupied by a substance • Usually measured in L (liquids and gases) 1 cm3 = 1 mL 1 dm3 = 1 L = 1000 mL 1 m3 = 1000 L

  4. Volume, Pressure & Temperature Volume: Total space occupied by a substance Indicate, in each pair, which object has a higher gas volume, and why (same gas always).

  5. Volume, Pressure & Temperature Pressure: Force applied per unit of area (P = F/A) • The pressure of a gas results from the collisions of the gas molecules with the walls of the container • Pressure of a gas increaseswhen the number of moles of gasincreases • Pressureof a gas increases when temperatureincreases • Pressure of a gas increases when volumedecreases

  6. Volume, Pressure & Temperature Pressure: Force applied per unit of area (P = F/A) • Can be measured in different units 1 atm = 101.3 kPa *Standard Pressure 1 atm = 760 mm Hg 1 atm = 1013 mbar • Can be measured with a barometer (atmospheric pressure) or a manometer (gas pressure in closed container)

  7. Volume, Pressure & Temperature Pressure: Force applied per unit of area (P = F/A) If the same person is wearing these shoes when stepping on somebody’s foot: which heel would exert more pressure? Why?

  8. Volume, Pressure & Temperature Pressure: Force applied per unit of area (P = F/A) How could you lower the pressure applied by this truck on the road? Explain.

  9. Volume, Pressure & Temperature Temperature:Manifestation of average kinetic energy of molecules of a gas Which gas is at a higher temperature? Explain.

  10. Volume, Pressure & Temperature Boyle’s law: At constant temperature, the volume of a given quantity of gas is inversely proportional to its pressure PV = k (k: constant) or P1V1 = P2V2

  11. Volume, Pressure & Temperature Example: You need to put the equivalent of 400 L of air at standard pressure to go scuba- diving. If your tank’s capacity is only 11.4 L, what pressure will be needed in it assuming that temperature is constant?

  12. Volume, Pressure & Temperature

  13. Volume, Pressure & Temperature

  14. Volume, Pressure & Temperature

  15. Volume, Pressure & Temperature Kelvin’s absolute temperature: • At T = 0°C, T = 273K • T(K) = T(°C) + 273 Freezing point of Water: T(K) = T(°C) + 273 T(K) = 0°C + 273 T(K) = 273K Boiling point of Water: T(K) = T(°C) + 273 T(K) = 100°C + 273 T(K) = 373K

  16. Volume, Pressure & Temperature Charles’s law: At constant pressure, the volume of a given quantity of gas is directly proportional to its temperature V/T (K) = k (k: constant) or V1 / T1(K) = V2 /T2 (K) *T(K): temperature in Kelvin T(K) and n must be constant

  17. Volume, Pressure & Temperature Combining Boyle’s & Charles’s law: At constant volume, the pressure of a given quantity of gas is directly proportional to its temperature P/T (K) = k (k: constant) or P1 / T1(K) = P2 /T2 (K) *T(K): temperature in Kelvin T(K) and n must be constant

  18. Volume, Pressure & Temperature When temperature increases in a room (external factor): _The volume (internal factor) of a gas trapped in a container increases, as molecules will move faster, collisions will increase and expansion will occur. _The pressure(internal factor) will also increase because molecules will move faster and therefore collide with walls of recipient with higher force. It all leads to an EXPLOSION!

  19. Volume, Pressure & Temperature Example: The volume of a given gas sample is 1.56L at -70°C. What will its volume be at 2°C if the pressure of the system remains constant?

  20. Volume, Pressure & Temperature Yes. The speed (and thus kinetic energy) of gas molecules has increased as a result of the increase in temperature Volume does not change (can) Pressure increased as the energy given to molecules (by the increase of temperature) increased their velocity (Ek) and so their collisions with walls would increase, thus increasing pressure (P=F/A) No, it does not. It only applies when volume is allowed to change as a result of a change in temperature, at constant pressure.

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