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The Gaseous State of MatterChapter 12 Hein and Arena Dr. Eugene PasserChemistry DepartmentBronx Community College © John Wiley and Company Version 1.1
The Kinetic-Molecular Theory • KMT is based on the motions of gas particles. • A gas that behaves exactly as outlined by KMT is known as an ideal gas. • While no ideal gases are found in nature, real gases can approximate ideal gas behavior under certain conditions of temperature and pressure.
Principle Assumptions of the KMT • Gases consist of tiny particles. • The distance between particles is large compared with the size of the particles themselves. • Gas particles have no attraction for one another.
Principle Assumptions of the KMT • Gas particles move in straight lines in all directions, colliding frequently with one another and with the walls of the container. • No energy is lost by the collision of a gas particle with another gas particle or with the walls of the container. All collisions are perfectly elastic.
Principle Assumptions of the KMT • The average kinetic energy for particles is the same for all gases at the same temperature, and its value is directly proportional to the Kelvin temperature.
Stopcock closed No diffusion occurs Stopcock open Diffusion occurs Diffusion The ability of two or more gases to mix spontaneously until they form a uniform mixture.
STP Standard Conditions Standard Temperature and Pressure Standard Temperature and Pressure Selected common reference points of temperature and pressure. 273.15 K or 0.00oC 1 atm or 760 torr or 760 mm Hg
Volume of one mole of any gas at STP = 22.4 L. • 22.4 L at STP is known as the molar volume of any gas.
The density of neon at STP is 0.900 g/L. What is the molar mass of neon?
nT V a P
atmospheres nT V a P
liters nT V a P
moles nT V a P
Kelvin nT V a P
nT Ideal Gas Constant V a P
A balloon filled with 5.00 moles of helium gas is at a temperature of 25oC. The atmospheric pressure is 750. torr. What is the balloon’s volume? Step 1. Organize the given information. Convert temperature to kelvins. K = oC + 273 K = 25oC + 273 = 298K Convert pressure to atmospheres.
A balloon filled with 5.00 moles of helium gas is at a temperature of 25oC. The atmospheric pressure is 750. torr. What is the balloon’s volume? Step 2. Write and solve the ideal gas equation for the unknown. Step 3. Substitute the given data into the equation and calculate.
Determination of Molecular Weights Using the Ideal Gas Equation
Calculate the molar mass of an unknown gas, if 0.020 g occupies 250 mL at a temperature of 305 K and a pressure of 0.045 atm. V = 250 mL = 0.250 L g = 0.020 g P = 0.045 atm T = 305 K
Gas Stoichiometry Primary conversions involved in stoichiometry.
What volume of oxygen (at STP) can be formed from 0.500 mol of potassium chlorate? The problem can be solved in one continuous calculation. 2 KClO3 2KCl + 3 O2
nT V a P
What volume of hydrogen, collected at 30.0oC and 700. torr, will be formed by reacting 50.0 g of aluminum with hydrochloric acid? 2 Al(s) + 6 HCl(aq) 2AlCl3(aq) + 3 H2(g) Step 1 Calculate moles of H2. grams Al moles Al moles H2
What volume of hydrogen, collected at 30.0oC and 700. torr, will be formed by reacting 50.0 g of aluminum with hydrochloric acid? 2 Al(s) + 6 HCl(aq) 2AlCl3(aq) + 3 H2(g) Step 2 Calculate liters of H2. • Convert oC to K: 30.oC + 273 = 303 K • Convert torr to atm:
What volume of hydrogen, collected at 30.0oC and 700. torr, will be formed by reacting 50.0 g of aluminum with hydrochloric acid? • Solve the ideal gas equation for V PV = nRT
Real Gases • Deviations from the gas laws occur at high pressures and low temperatures. • At high pressures the volumes of the real gas molecules are not negligible compared to the volume of the gas • At low temperatures the kinetic energy of the gas molecules cannot completely overcome the intermolecular attractive forces between the molecules.
