Physical Properties Gases

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

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

Characteristics of Gases b 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 Temperature ºF ºC K K = ºC b Always use the Kelvin scale when working with gases.

Pressure Pressure Which shoes create the most pressure?

Pressure Pressure Barometer measures atmospheric pressure Mercury Barometer Aneroid Barometer

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

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

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

b Answers 300 K 223 K 0 K

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

b Answers 0 °C 77 °C -173 °C -253 °C

Pressure Conversions 1. Convert 109 kPa to atm 2. Convert 0.62 atm to mm Hg 3. Convert atm to kPa 4. Convert mmHg to kPa

b Answers atm mm Hg kPa kPa

The Gas Laws Gases

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

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

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

Combined Gas Law Combined Gas Law P1V1T1P1V1T1 = P2V2T2P2V2T2 P 1 V 1 T 2 = P 2 V 2 T 1

GIVEN: V 1 = 473 cm 3 T 1 = 36°C = 309K V 2 = ? T 2 = 94°C = 367K WORK: P 1 V 1 T 2 = P 2 V 2 T 1 Gas Law Problems b A gas occupies 473 cm 3 at 36°C. Find its volume at 94°C. TT VV (473 cm 3 )(367 K)=V 2 (309 K) V 2 = 562 cm 3

GIVEN: V 1 = 100. mL P 1 = 150. kPa V 2 = ? P 2 = 200. kPa WORK: P 1 V 1 T 2 = P 2 V 2 T 1 Gas Law Problems b A gas occupies 100. mL at 150. kPa. Find its volume at 200. kPa. PP VV (150.kPa)(100.mL)=(200.kPa)V 2 V 2 = 75.0 mL

GIVEN: V 1 = 7.84 cm 3 P 1 = 71.8 kPa T 1 = 25°C = 298 K V2 = ?V2 = ? P 2 = kPa T 2 = 273 K WORK: P 1 V 1 T 2 = P 2 V 2 T 1 (71.8 kPa)(7.84 cm 3 )(273 K) =( kPa) V 2 (298 K) V 2 = 5.09 cm 3 Gas Law Problems b A gas occupies 7.84 cm 3 at 71.8 kPa & 25°C. Find its volume at STP. P  T  VV

GIVEN: P 1 = 765 torr T 1 = 23°C = 296K P 2 = 560. torr T 2 = ? WORK: P 1 V 1 T 2 = P 2 V 2 T 1 Gas Law Problems b A gas’ pressure is 765 torr at 23°C. At what temperature will the pressure be 560. torr? PP TT (765 torr)T 2 = (560. torr)(296K) T 2 = 217 K = -56°C