Chem 110 05 Gases

Slide 1 :Chapter 05 Gases


Slide 2 :Nature and Properties of Gases Gases have the following physical characteristics Gases assume the volume and shape of their containers Gases are the most compressible of the states of matter Gases will mix evenly and completely when confined to the same container Gases have much lower densities than liquids and solids.


Slide 3 :Pressure of a Gas Pressure (p) is the force over an area applied to an object in a direction perpendicular to the surface The SI unit of pressure is the pascal (Pa), defined as one newton per square meter.


Slide 4 :Atmospheric Pressure Atmospheric Pressure is the pressure exerted by Earth’s atmosphere.


Slide 5 :Barometer Barometer is an instrument used for measuring atmospheric pressure.


Slide 6 :Standard Atmospheric Pressure Standard Atmospheric Pressure (1atm) is equal to the pressure that supports a column of mercury exactly 760 mm (or 76 cm) high at 0°C at sea level.


Slide 7 :Manometer Manometer is a device used to measure the pressure of gases other than the atmosphere. Two types of Manometers Closed-Tube Manometer Open-Tube Manometer


Slide 8 :Example 5.1 The pressure outside a jet plane flying at high altitude falls considerably below standard atmospheric pressure. Therefore, the air inside the cabin must be pressurized to protect the passengers. What is the pressure in atmospheres in the cabin if the barometer reading is 688 mmHg? 0.905 atm How To Convert Different Pressure Units


Slide 9 :Boyle's Law


Slide 10 :Charles’ Law


Slide 11 :Gay-Lussac's Law


Slide 12 :Avogadro's Law


Slide 13 :Ideal Gas Equation Ideal Gas is a hypothetical gas whose pressure-volume-temperature behavior can be completely accounted for by the ideal gas equation. The molecules of an ideal gas do not attract or repel one another, and their volume is negligible compared to the volume of the container. R is the universal gas constant which is equivalent to 0.0821 L·atm/mol·K


Slide 14 :Example 5.2 Sulfur hexafluoride (SF6) is a colorless, odorless, very unreactive gas. Calculate the pressure (in atm) exerted by 1.82 moles of the gas in a steel vessel of volume 5.43 L at 45°C. P = 8.75 atm Using the ideal Gas Law


Slide 15 :Volume of an Ideal Gas at STP Standard Temperature and Pressure (STP) is when conditions are 0°C and 1atm The volume of 1 mole any gaseous substance at STP is 22.4 Liters. Thus it is also called the molar volume.


Slide 16 :Example 5.3 Calculate the volume (in liters) occupied by 7.40 g of NH3 at STP. V = 9.73 L Standard Temperature and Pressure


Slide 17 :Combined Gas Laws


Slide 18 :Example 5.4 A small bubble rises from the bottom of a lake, where the temperature and pressure are 8°C and 6.4 atm, to the water’s surface, where the temperature is 25°C and the pressure is 1.0 0 atm. Calculate the final volume (in mL) of the bubble if its initial volume was 2.1 mL. V2 = 14 L Using the Combined Gas Law


Slide 19 :Density and Molar Mass of a Gaseous Substance


Slide 20 :Example 5.5 A chemist has synthesized a greenish-yellow gaseous compound of chlorine and oxygen and finds that its density is 7.71 g/L at 36°C and 2.88 atm. Calculate the molar mass of the compound and determine its molecular formula. M = 67.9 g/mol Molecular Formula = ClO2 Density in the Ideal Gas Equation


Slide 21 :Gas Stoichiometry Mass reactants  moles of reactants  moles of products  ideal gas equation


Slide 22 :Example 5.6 Sodium azide (NaN3) is used in some automobile air bags. The impact of collision triggers the decomposition of NaN3 as follows 2NaN3  2Na + 3N2 The nitrogen gas produced quickly inflates the bag between the driver and the windshield and dashboard. Calculate the volume of N2 generated at 80°C and 823 mmHg by the decomposition of 60.0 g of NaN3. V = 37.0 L Gas Stoichiometry


Slide 23 :Dalton’s Law of Partial Pressures Partial pressure is the pressure of individual gas components in the mixture. Dalton’s Law of Partial Pressures states that “The total pressure of a mixture of gases is just the sum of the pressures that each gas would exert if it were present alone.” Mole fraction is a dimensionless quantity that expresses the ratio of the number of moles of one component (ni) to the number of moles of all components present (nT).


Slide 24 :Example 5.7 A mixture of gases contains 4.46 moles of neon (Ne), 0.74 mole of argon (Ar), and 2.15 moles of xenon (Xe). Calculate the partial pressures of the gases if the totla pressure is 2.00 atm at a certain temperature. PNe = 1.21 atm PAr = 0.20 atm PXe = 0.586 atm Partial Pressure and Mole Fraction


Slide 25 :Example 5.8 Oxygen gas generated by the decomposition of potassium chlorate is collected. The volume of oxygen collected at 24C and atmospheric presssure of 762 mmHg is 128 mL. Calculate the mass (in grams) of oxygen gas obtained. The pressure of the water vapor at 24°C is 22.4 mmHg. m = 0.164 g Using the ideal gas equation in calculating for the mass of a collected gas


Slide 26 :Kinetic Molecular Theory of Gases Kinetic Molecular Theory of Gases A gas consists of tiny particles, either atoms or molecules, moving about at random. The volume of the particles themselves is negligible compared with the total volume of the gas; most of the volume of a gas is empty space. The gas particles act independently of one another; there are no attractive or repulsive forces between particles. Collisions of the gas particles, either with other particles or with the walls of a container, are elastic (constant temperature). The average kinetic energy of the gas particles is proportional to the Kelvin temperature of the sample.


Slide 27 :Example 5.9 Calculate the root-mean-square of helium atoms and nitrogen molecules in m/s at 25°C. urms= 1.36 x 103 m/s urms = 515 m/s Calculating the root-mean-square of the atoms and molecules


Slide 28 :Graham’s Law of Diffusion Diffusion is the gradual mixing of molecules of one gas with molecules of one gas with molecules of another by virtue of their kinetic properties Graham’s Law of Diffusion states that “Under the same conditions of temperature and pressure, rates of diffusion for gases are inversely proportional to the square roots of their molar masses.” Effusion is the process by which a gas under pressure escapes from one compartment of a container to another by passing through a small opening.


Slide 29 :Example 5.10 A flammable gas made up only of carbon and hydrogen is found to effuse through a porous barrier in 1.50 min. Under the same conditions of temperature and pressure, it takes an equal volume of bromine vapor 4.73 min to effuse through the same barrier. Calculate the molar mass of the unknown gas, and suggest what the gas might be. M = 16.1 g/mol CH4 Gas Effusion


Slide 30 :Deviation from Ideal Behavior Van der Waals Equation


Slide 31 :Example 5.11 Given that 3.50 moles of NH3 occupy 5.20 L at 47C, calculate the pressure of the gas (in atm) using (a) the ideal gas equation and (b) the van der Waals equation. (correction terms a = 4.17 atm·L2/mol2 and b = 0.0371 L/mol) P = 17.7 atm P = 16.3 atm Comparison of Ideal and Van der Waals Gas Equations