BellringerBellringer b An average human heart beats 60 times per minute. If the average person lives to the age of 75, how many times does the average heart beat? b A certain laser printer can print 12 pages per minute. Determine this printer’s output in pages per day, and reams per month. (1 ream = 5000 pages)

I. Physical Properties Ch Gases

A. Ideal Gas vs. Real Gas b Kinetic Molecular Theory (KMT) The theory that explains the behavior of gases at the molecular level. This theory makes some assumptions about a theoretical gas called an ideal gas.

A. Ideal Gas vs. Real Gas

Gas behavior is most ideal… at low pressures at high temperatures in nonpolar atoms/molecules  (see picture)

B. Characteristics of Gases 1. Gases expand to fill any container. 2. Gases are fluids (like liquids). 3. Gases can be compressed. 4. Gases exert pressure. 5. Gases undergo diffusion & effusion.

B. Characteristics of Gases b Diffusion Spreading of gas molecules throughout a container until evenly distributed. b Effusion Passing of gas molecules through a tiny opening in a container.

C. Temperature ºC K b Always use absolute temperature (Kelvin) when working with gases. Gases have an avg. KE directly related to Kelvin temperature. If temp. goes up, KE goes up.

D. Pressure Which shoes create the most pressure? SI unit for pressure is the Pascal: 1 Pa =Newton(N)/m 2

D. Pressure b Barometer: Measures atmospheric pressure b The pressure of the atmosphere at sea level will hold a column of mercury 760 mm Hg. b Meridan, ID: pressure = 745 mm Hg 1 atm Pressure 760 mm Hg Vacuum

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

D. Pressure 1. The column of mercury in a barometer is 745 mm high. What is the atmospheric pressure in kPa? 745 mm Hg kPa 760 mm Hg = 99.3 kPa

E. STP Standard Temperature & Pressure 0°C 273 K 1 atm Or kPa Or … Or STP

Describe the behavior of gases in regards to Pressure, Volume, & Temperature F. The Gas Laws:

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

V T Charles’ Law 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

V n Avogadro’s Law Avogadro’s Law b Equal volumes of gases contain equal numbers of moles (n) at constant temp & pressure true for any gas

Combined Gas Law P1V1n1T1P1V1n1T1 = P2V2n2T2P2V2n2T2 P 1 V 1 = P 2 V 2 What other equations?

GIVEN: V 1 = 473 cm 3 T 1 = 36°C = 309K V 2 = ? T 2 = 94°C = 367K WORK: V 1 / T 1 = V 2 / T 2 G. Gas Law Problems b A gas occupies 473 cm 3 at 36°C. Find its volume at 94°C. CHARLES’ LAW TT VV 473 cm 3 )/(309 K)=V 2 /(367 K) V 2 = 562 cm 3

GIVEN: V 1 = 100. mL P 1 = 150. kPa V 2 = ? P 2 = 1.50 x10 3 mmHg = 200. kPa WORK: P 1 V 1 = P 2 V 2 G. Gas Law Problems b A gas occupies 100. mL at 150. kPa. Find its volume at 1.50 x10 3 mm Hg. BOYLE’S LAW 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 = P 2 V 2 (71.8 kPa)(7.84 cm 3 )/(298 K) =( kPa) V 2 /(273 K) V 2 = 5.09 cm 3 G. 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 COMBINED GAS LAW T 1 T 2

GIVEN: P 1 = 2.25 atm T 1 = 20°C = 293K P 2 = ? T 2 = 45°C = 318K WORK: P 1 /T 1 = P 2 /T 2 E. Gas Law Problems b On a spring morning, 20°C, you fill your tires to a pressure of 2.25 atm. As you ride along, the tire heats up to 45°C from the friction on the road. What is the pressure in the tires now in units of psi? GAY-LUSSAC’S LAW PP TT (2.25 atm)/(293 K) = ( ?)/ (318 K) P 2 = 2.44 atm = 35.9 psi

F. Dalton’s Law b The total pressure of a mixture of gases equals the sum of the partial pressures of the individual gases. P total = P 1 + P When a H 2 gas is collected by water displacement, the gas in the collection bottle is actually a mixture of H 2 and water vapor.

F. Dalton’s Law & Water Displacement P total = P gas + P water vapor Measured at several temps. (see chart)

GIVEN: P gas = ? P total = mm Hg P H2O = mm Hg WORK: P total = P gas + P H2O mm = P gas mm P gas = mm Hg b A gas is collected over water at a temp of 35.0°C when the barometric pressure is mm Hg. What is the partial pressure of the dry gas? Look up water-vapor pressure on the chart for 35.0°C. Sig Figs: Round to least number of decimal places. F. Dalton’s Law The total pressure in the collection bottle is equal to barometric pressure and is a mixture of the “gas” and water vapor.

GIVEN: P H2 = ? P total = 94.4 kPa P H2O = mmHg WORK: P total = P H2 + P H2O 94.4 kPa = P H kPa P H2 = 91.8 kPa F. Dalton’s Law b Hydrogen gas is collected over water at 22°C. Find the pressure of the dry gas if the atmospheric pressure is 94.4 kPa. Look up water-vapor pressure and convert for 22°C. Sig Figs: Round to least number of decimal places. The total pressure in the collection bottle is equal to atmospheric pressure and is a mixture of H 2 and water vapor.