1. Avogadros’ and the Ideal Gas Law CHEMISTRY

2. Vocabulary & Unit Conversions Pressure is the force exerted per area Gases exert pressure when they collide with the sides of a container. More collisions = more pressure. Pressure is measured with a barometer. 1 atm = 101.3 kPa 1 atm = 760 mm Hg or torr Rigid means that the volume is constant

3. Standard Temperature and Pressure (STP) The volume of a sample of gas changes with temperature and pressure, so scientists have defined standards for temperature and pressure. Standard temperature is 0 o C or 273 K. Standard pressure is 1 atm or 101.3 kPa. Remember at STP one mole of any gas has a volume of 22.4 L!!!

4. P 1 V 1 = P 2 V 2 T 1 T 2 One mole of methane is at STP. What volume would it occupy at 25 o C and 107.8 kPa?

5. Avogadro’s Law

6. Equal volumes of gas at the same temperature and pressure contain the same number of molecules. ( 1 mole of any gas at STP has a volume of 22.4 L)

7. The volume of a sample of gas is directly proportional to the number of molecules present, or moles of gas. As moles (n), volume (V).

8. I 2 (g) + H 2 (g)  2HI(g) For gases, the coefficients give the volume ratio in which the substances react. THIS ONLY APPLIES TO GASES!!!!

9. N 2 (g) + 3H 2 (g)  2NH 3 (g) If 3.4 L nitrogen reacts with excess hydrogen what volume ammonia would be produced at STP?

10. Ideal Gas Law RELATES THE PRESSURE, VOLUME TEMPERATURE AND MOLES OF A SAMPLE OF GAS.

11. An ideal gas is a gas that follows KMT exactly. That is the molecules have no attractions, so that it would remain a gas down to absolute zero. And The molecules have no volume, so that the gas would have no volume at absolute zero.

12. Ideal gases do not exist! The molecules of a real gas do attract each other as they are cooled down. This is why real gases become liquids. Real gas molecules also have some volume, and do occupy space at lower temperatures.

13. If ideal gases do not exist, then why is there an ideal gas law? At high temperatures and low pressures real gases behave ideally. At high temperatures molecules have enough kinetic energy to overcome attractive forces. At low pressure the gas molecules are so far apart that the volume is negligible. Most gases at STP behave ideally. 273 K is a “high” temperature and 1 atm is a low enough pressure.

14. PV = nRT Where: P is pressure in kPa V is volume in L n is moles of gas T is the temperature in K and R is the universal gas constant R = 8.314 L*kPa / mole*K

15. Benefit of the ideal gas law – you only need to measure quantities under one set of conditions. Difficulty – the units for measuring each quantity must match R!!

16. PV = nRT R = 8.314 L kPa / mole K What volume would 4.5 mole of hydrogen occupy at 25 C and 104.6 kPa?

17. PV = nRT R = 8.314 L kPa / mole K What mass of methane, CH 4, would occupy 3.00 L at STP?

18. What volume of methane, CH 4, has a mass of 34.5g if the temperature is 35 C and the pressure is 454 kPa?

19. What volume would 7.98 g of nitrogen gas occupy at 103.5 kPa and 25 C?

20. What mass in grams of oxygen, O 2, would be needed to fill a 500.0 mL container at 22.0 C to a pressure of 113 kPa?