2. Gas Variables Physical CharacteristicsTypical Units Volume, Vliters (L) Pressure, P atmosphere ( 1 atm=101.3 kPa=760 Torr ) Temperature, TKelvin (K) Number of atoms or molecules, n mole (1 mol = 6.022x10 23 atoms or molecules)

3. Showed that Pressure influences the volume of a gas during a controlled experiment. Robert Boyle Ireland January 25, 1627 – December 30, 1690

4. Boyle's experiment Torricelli's experiment did more than just show that air has weight; it also provided a way of creating a vacuum because the space above the column of mercury at the top of the barometer is almost completely empty. (It is free of air or other gases except a negligible amount of mercury vapor.) Torricelli's work with a vacuum soon caught the eye of the British scientist Robert Boyle.

5. Boyle's Experiment Boyle's most famous experiments with gases dealt with what he called the "spring of air." These experiments were based on the observation that gases are elastic. (They return to their original size and shape after being stretched or squeezed.) Boyle studied the elasticity of gases in a J-tube similar to the apparatus shown in the figure below. By adding mercury to the open end of the tube, he trapped a small volume of air in the sealed end. Trapped air

6. Boyle’s Law: P 1 V 1 = P 2 V 2

8. PV = k A Boyle’s law graph will always have a ½ hyperbola shape. Illustrated by the equation  PV = k Volume and pressure are inversely proportional. If one increases the other decreases. Boyle’s Law: P 1 V 1 = P 2 V 2

9. Boyle's Law The pressure of a gas is inversely related to the volume when the Temperature does not change Then the PV product remains constant P 1 V 1 = P 2 V 2

10. A Boyle’s Law Problem Freon-12, (CCl 2 F 2 ), is used in refrigeration systems. What is the new volume (L) of a 1.6 L sample of Freon gas initially at 50 mm Hg after its pressure is changed to 200 mm Hg at constant T? Initial conditions Final conditions P 1 = 50 mm HgP 2 = 200 mm Hg V 1 = 1.6 LV 2 = ? V 2 = 1.6 L x 50 mm Hg = 0.4 L 200 mm Hg 200 mm Hg

11. Jaques Charles Charles invented the hydrogen-filled balloon and on December 1, 1783, he ascended into the air and became possibly the first man in history to witness a double sunset

12. Jaques Charles Jacques Charles carried out experiments in 1786 and 1787 that showed a direct relationship between the temperature and volume of gases at constant pressure. You know that most matter expands as its temperature rises. Gases are no different. When Benjamin Thomson and Lord Kelvin proposed an absolute temperature scale in 1848, it was possible to set up the mathematical expression of Charles’s law.

13. Charles’ Law: V and T Charles’s law states that the volume of a sample of gas is directly proportional to the absolute temperature when pressure remains constant.

14. Charles’ Law Compares the V and T of Confined gases How does volume change with temperature? V 1 = 125 mL V 2 = 250 mL T 1 = 273 K T 2 = 546 K 1 mole of gas & Pressure = 753 mmHg D

15. V and T Problem A balloon has a volume of 785 mL on a Fall day when the temperature is 21°C. In the winter, the gas cools to 0°C. What is the new volume of the balloon?

16. VT Calculation Initial conditionsFinal conditions V 1 = 785 mLV 2 = ? 294 K273 K T 1 = 21°C = 294 KT 2 = 0°C = 273 K V 2 = _______ mL x __ K = _______ mL K Check your answer: If temperature decreases, V should decrease. 273 294 785 728.9

17. Charles Law A sample of oxygen gas has a volume of 420 mL at a temperature of 18°C. What temperature (in °C) is needed to change the volume to 640 mL? 1) 443°C2) 170°C 3) - 82°C 2) 170°C

18. Solution 2) 170°C A sample of oxygen gas has a volume of 420 mL at a temperature of 18°C. What temperature (in °C) is needed to change the volume to 640 mL? T 2 = V 2 T 1 V 1 V 1 T 2 = 640 mL x 291 K = 443 K 420 mL T 2 = 443 K - 273 K = 170°C

19. Gay-Lussac’s Law Joseph Louis Gay-Lussac in 1802 made reference in his paper to unpublished work done by Jacques Charles. Charles had found that oxygen, nitrogen, hydrogen, carbon dioxide, and plain air expand to the same extent over the same 80 degree interval.

20. Gay-Lussac Gay-Lussac was no slouch in the area of ballooning. On September 16, 1804, he ascended to an altitude of 7016 meters (just over 23,000 feet - about 4.3 miles). This remained the world altitude record for almost 50 years.

21. Gay-Lussac’s law: The Pressure of a sample of gas at constant volume will vary directly with absolute (Kelvin) temperature The Pressure of a sample of gas at constant volume will vary directly with absolute (Kelvin) temperature. Temperature & pressure  As P  then T   At constant Volume & moles