Gases Physical Properties

Kinetic Molecular Theory Particles in an ideal gas… have no volume. The particles in a gas are very far apart. have elastic collisions. are in constant, random, straight-line motion. don’t attract or repel each other. have an avg. KE directly related to Kelvin temperature.

Real Gases Particles in a REAL gas… have their own volume attract each other Gas behavior is most ideal… at low pressures at high temperatures

Characteristics of Gases Gases expand to fill any container. Gases have very low densities. no volume = lots of empty space Gases can be compressed Compressibility—a measure of how much the volume of matter decreases under pressure

Characteristics of Gases Gases undergo diffusion & effusion. Diffusion –the tendency of molecules to go from areas of high concentration to area of low concentration Effusion – the process when a gas escapes through a tiny hole in a container

Temperature Always use the Kelvin scale when working with gases. ºF ºC K -459 32 212 -273 100 273 373 K = ºC + 273

Pressure Which shoes create the most pressure?

Pressure KEY UNITS AT SEA LEVEL 101.325 kPa (kilopascal) 1 atm 760 mm Hg 760 torr 14.7 psi

Standard Temperature & Pressure STP STP Standard Temperature & Pressure 0°C 273 K 1 atm 101.325 kPa -OR-

Temperature Conversions Convert each of the following to Kelvin temperatures 27 °C -50 °C -273 °C

Answers 300 K 223 K 0 K

Temperature Conversions Convert each of the following to degrees Celsius 273 K 350. K 100. K 20. K

Answers 0 °C 77 °C -173 °C -253 °C

Pressure Conversions Convert 109 kPa to atm Convert 0.62 atm to mm Hg Convert 0.3587 atm to kPa Convert 29.32 mmHg to kPa

Answers 1.08 atm 470 mm Hg 36.345 kPa 3.91 kPa

Gases The Gas Laws P V T

Boyle’s Law The pressure and volume of a gas are inversely related at constant mass & temp P V

Charles’ Law The volume and absolute temperature (K) of a gas are directly related at constant mass & pressure V T

Gay-Lussac’s Law The pressure and absolute temperature (K) of a gas are directly related at constant mass & volume P T

Combined Gas Law P1V1 T1 = P2V2 T2 P1V1T2 = P2V2T1

Gas Law Problems A gas occupies 473 cm3 at 36°C. Find its volume at 94°C. GIVEN: V1 = 473 cm3 T1 = 36°C = 309K V2 = ? T2 = 94°C = 367K T V WORK: P1V1T2 = P2V2T1 (473 cm3)(367 K)=V2(309 K) V2 = 562 cm3

Gas Law Problems A gas occupies 100. mL at 150. kPa. Find its volume at 200. kPa. GIVEN: V1 = 100. mL P1 = 150. kPa V2 = ? P2 = 200. kPa P V WORK: P1V1T2 = P2V2T1 (150.kPa)(100.mL)=(200.kPa)V2 V2 = 75.0 mL

Gas Law Problems P T V V1 = 7.84 cm3 P1 = 71.8 kPa A gas occupies 7.84 cm3 at 71.8 kPa & 25°C. Find its volume at STP. GIVEN: V1 = 7.84 cm3 P1 = 71.8 kPa T1 = 25°C = 298 K V2 = ? P2 = 101.325 kPa T2 = 273 K P T V WORK: P1V1T2 = P2V2T1 (71.8 kPa)(7.84 cm3)(273 K) =(101.325 kPa) V2 (298 K) V2 = 5.09 cm3

Gas Law Problems A gas’ pressure is 765 torr at 23°C. At what temperature will the pressure be 560. torr? GIVEN: P1 = 765 torr T1 = 23°C = 296K P2 = 560. torr T2 = ? P T WORK: P1V1T2 = P2V2T1 (765 torr)T2 = (560. torr)(296K) T2 = 217 K = -56°C