Gases

Gases I. Physical Properties

A. Characteristics of Gases expand to fill any container fluids (like liquids) have very low densities

A. Characteristics of Gases can be compressed undergo diffusion & effusion

K = ºC + 273 B. Temperature always use KELVIN when working with gases ºF ºC K -459 32 212 -273 100 273 373 K = ºC + 273

C. Pressure Which shoes create the most pressure?

C. Pressure barometer measures atmospheric pressure Aneroid Barometer Mercury Barometer Aneroid Barometer

C. Pressure manometer measures contained gas pressure U-tube Manometer Bourdon-tube gauge

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

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

Gases II. The Gas Laws P V T

P1V1 = P2V2 A. Boyle’s Law inverse relation! example: car engine cylinder breathing inverse relation! P V

A. Boyle’s Law

proportional relation! B. Charles’ Law example: hot air balloons V1 = V2 T1 T2 proportional relation! V T

B. Charles’ Law

proportional relation! C. Gay-Lussac’s Law example: autoclave (sterlization) P1 = P2 T1 T2 proportional relation! P T

D. Combined Gas Law P1V1 T1 = P2V2 T2 P1V1T2 = P2V2T1

E. Gas Law Problem #1 A gas occupies 473 cm3 at 36°C. Find its volume at 94°C.

E. Gas Law Problem #2 A gas occupies 100. mL at 150. kPa. Find its volume at 200. kPa.

E. Gas Law Problem #3 A gas occupies 7.84 cm3 at 71.8 kPa & 25°C. Find its volume at STP.

E. Gas Law Problem #4 A gas’ pressure is 765 torr at 23°C. At what temperature will the pressure be 560. torr?

Gases Ideal Gas Law

Avogadro’s Principle CO2 Ne Equal volumes of gases contain equal numbers of moles at constant temp & pressure true for any gas V n

UNIVERSAL GAS CONSTANT Ideal Gas Law PV=nRT UNIVERSAL GAS CONSTANT R=0.0821 Latm/molK

Ideal Gas Law Problem #5 Calculate the pressure in atmospheres of 0.412 mol of He at 16°C & occupying 3.25 L.

Ideal Gas Law Problem #6 Find the volume of 85 g of O2 at 25°C and 104.5 kPa.

Gas Stoichiometry at Non-STP Conditions Gases Gas Stoichiometry at Non-STP Conditions

Gas Stoichiometry at STP: moles  liters of a gas: use 22.4 L = 1 mol How many moles are in a 4.5 L helium balloon at STP?

Gas Stoichiometry at STP: moles  liters of a gas: use 22.4 L = 1 mol __H2 + __O2  __H2O How many grams of water can be formed if you start with 2.3 L of H2?

Gas Stoichiometry at non-STP given liters of gas? start with ideal gas law looking for liters of gas? start with stoichiometry conv.

Gas Stoichiometry Problem What volume of CO2 forms from the decomposition of 5.25 g of CaCO3 at 103 kPa & 25ºC? CaCO3  CaO + CO2

Gas Stoichiometry Problem What volume of CO2 forms from 5.25 g of CaCO3 at 103 kPa & 25ºC?

Gas Stoichiometry Problem How many grams of Al2O3 are formed from 15.0 L of O2 at 97.3 kPa & 21°C? 4 Al + 3 O2  2 Al2O3

Gas Stoichiometry Problem How many grams of Al2O3 are formed from 15.0 L of O2 at 97.3 kPa & 21°C? 4 Al + 3 O2  2 Al2O3

Gases Two More Laws

Ptotal = P1 + P2 + ... Dalton’s Law The total pressure of a mixture of gases equals the sum of the partial pressures of the individual gases. Ptotal = P1 + P2 + ... When H2 gas is collected by water displacement, the gas in the collection bottle is actually a mixture of H2 and water vapor.

Dalton’s Law Hydrogen gas is collected over water at 22.5°C. Find the pressure of the dry gas if the atmospheric pressure is 94.4 kPa.

Dalton’s Law A gas is collected over water at a temp of 35.0°C when the barometric pressure is 742.0 torr. What is the partial pressure of the dry gas?

Graham’s Law diffusion spreading of gas molecules throughout a container until evenly distributed effusion passing of gas molecules through a tiny opening in a container

Graham’s Law speed of diffusion/effusion KE is determined by temp of gas at same temp & KE, heavier molecules move more slowly

Graham’s Law Graham’s Law rate of diffusion of a gas is inversely related to square root of molar mass

Graham’s Law Determine the relative rate of diffusion for krypton and bromine.

Graham’s Law A molecule of oxygen gas has an average speed of 12.3 m/s at a given temp and pressure. What is the average speed of hydrogen molecules at the same conditions?

Graham’s Law An unknown gas diffuses 4.0 times faster than O2. Find its molar mass.