Chapter 5 Nov 6 1:02 PM Expand to fill their containers Fluid motion (they flow) Have low densities (1/1000 the density of equivalent liquids or solids) Compressible Can Effuse and Diffuse Effuse: The passage of a gas through a tiny hole into an evacuated (vacuumed) chamber Diffusion: The mixing of gases (Spreading throughout a room) Nov 6 1:17 PM 1
Kinetic Molecular Theory Particles of matter are always in motion Collision of the particles with the walls is what causes pressure Particles are very small compared with the distance between them The volume of the individual particles can be assumed to be zero Particles exert no forces on each other The do not attract or repel each other (No IMFs) Average kinetic energy is proportional to temperature of a gas Temperature of a gas is measured in Kelvin Nov 6 1:26 PM Kinetic Molecular Theory Ideal Gas: Imaginary gases that perfectly fit all of the assumptions of the kinetic molecular theory Tiny particles that are very spread apart relative to their size Collisions between gas particles and between the particles and walls of the container are elastic collisions No kinetic energy is lost in elastic collisions There are no forces of attraction between the particles Particles are in constant, rapid motion (therefore possess kinetic energy) The average kinetic energy of particles depends on temperature, not the identity of the particles Nov 6 1:23 PM 2
Kinetic Molecular Theory Ideal versus real gases Tiny particles that are very spread apart relative to their size Low temperatures and high pressures Collisions between gas particles and between the particles and walls of the container are elastic collisions IMFs There are no forces of attraction between the particles IMFs Nov 6 1:23 PM Kinetic Molecular Theory Under which of the following conditions of temperature and pressure would 1.0 mol of the real gas CO 2 (g) behave most like an ideal gas? Temperature (K) Pressure (atm) a. 100 100 b. 800 0.1 c. 800 1 d. 800 100 Which of the following gases would be the least ideal? a. O 2 b. H 2 c. Br 2 d. Cl 2 Nov 6 1:23 PM 3
Pressure: The force created by the collisions of molecules with the walls of a container Pascal (Pa): SI Unit of pressure. 1 Pa = 1 N/M 2 Millimeter of Mercury (mm Hg): Pressure that supports a 1 mm column of mercury in a barometer Atmosphere (atm): Average atmospheric pressure at sea level and 0 Torr (torr): 1 torr = 1 mm Hg Nov 6 1:40 PM STP: Standard Temperature and Pressure Standard Pressure 1 Atm 101.3 kpa 14.7 lbs/in 2 760 mm Hg 760 torr Standard Temperature 273 K Nov 6 1:47 PM 4
Boyle's Law: Pressure is inversely proportional to volume when temperature is held constant Nov 6 1:55 PM Charles' Law: The volume of a gas is directly proportional to temperature (volume goes to zero when temperature is zero Kelvin) Nov 6 1:55 PM 5
Gay Lussac's Law: The pressure and temperature of a gas are directly related, provided that the volume remains constant Nov 6 1:55 PM Combined Gas Law: Combines all of the gas laws in one equation keeping the amount of gas constant Nov 6 1:55 PM 6
Ideal Gas Law: Relates the amount of gas to the pressure, volume and temperature of the gas PV = nrt P = pressure in atm V= volume in liters n = moles R = proportionality constant 0.0821 L*Atm/mol*K This can be different!!! T= Temperature in Kelvins Nov 6 2:06 PM Avagadro's Law: For a gas at constant temperature and pressure, the volume is directly proportional to the number of moles of gas (at low pressures) V = (a)(n) a = proportionality constant V = Volume of the gas n = number of moles of gas Nov 6 2:06 PM 7
Gas Density Molar volume at STP is 22.4L so at STP density is: Nov 6 2:12 PM How to Find Molar Mass of a Gas D = Mass Volume PV = nrt n = mass of gas molar mass Nov 6 2:17 PM 8
Dalton's Law of Partial Pressures: The total pressure of a mixture of gases is the addition of each pressure associated with each gas. P Total = P 1 + P 2 + P 3 +... Mole Fraction: X i = n i n total = P i P total Nov 9 7:33 AM A flask contains 0.25 mole of SO 2 (g), 0.50 mole of CH 4 (g), and 0.50 mole of O 2 (g). The total pressure of the gases in the flask is 800 mm Hg. What is the partial pressure of the SO 2 (g) in the flask? Nov 9 7:33 AM 9
Gas Stoichiometry If reactants and products are at the same temperature and pressure, then mole ratios of gases are also volume ratios 3 H 2 (g) + N 2 (g) 2NH 3 (g) 3 moles H 2 + 1 mole N 2 2 moles NH 3 3 liters H 2 + 1 liter N 2 2 liters NH 3 How many liters of ammonia can be produced when 12 liters of hydrogen react with an excess of nitrogen? How many liters of oxygen gas, at STP, can be collected from the complete decomposition of 50.0 grams of potassium chlorate? How many liters of oxygen gas, at 37.0C and 0.930 atmospheres, can be collected from the complete decomposition of 50.0 grams of potassium chlorate? Nov 6 2:04 PM Gas Stoichiometry A rigid 5.00 L cylinder contains 0.176 mol of NO(g) at 298 K. A 0.176 mol sample of O 2 (g) is added to the cylinder, when a reaction occurs to produce NO 2. a. Write the balanced equation for the reaction b. Calculate the total pressure, in atm, in the cylinder at 298 K after the reaction is complete. Nov 3 3:09 PM 10
At the same conditions of temperature, all gases have the same average kinetic energy. m = mass v = velocity At the same temperature, small molecules move FASTER than large molecules Nov 9 7:33 AM The experimental apparatus represented above is used to demonstrate the rates at which gases diffuse. When the cotton balls are placed in the ends of a tube at the same time, the gases diffuse from each end and meet somewhere in between, where they react to form a white solid. Which of the following combinations will produce a solid closes to the center of the tube? a. HCl and CH 3 NH 2 b. HCl and NH 3 c. HBr and CH 3 NH 2 d. HBr and NH 3 Nov 3 3:15 PM 11
A rigid 5.00 L cylinder contains 24.5 g of N 2 (g) and 28.0 g of O 2 (g) a. Calculate the total pressure, in atm, of the gas mixture in the cylinder at 298 K. b. The temperature of the gas mixture in the cylinder is decreased to 280 K. Calculate each of the following. i. The mole fraction of N 2 (g) in the cylinder. ii. The partial pressure, in atm, of N 2 (g) in the cylinder. c. If the cylinder develops a pinhole sized leak and some of the gaseous mixture escapes, would the ratio of N 2 /O 2 in the cylinder increase, decrease, or remain the same? Justify your answer. Nov 3 3:11 PM Maxwell Boltzmann Gas Distribution: Shows the average velocity of the gas sample due to the temperature of the gas Same amount of gas molecules for each line Nov 14 5:50 PM 12
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