Chapter 121 Gases

2 Characteristics of Gases -Expand to fill a volume (expandability) -Compressible -Readily forms homogeneous mixtures with other gases

Chapter 123 Pressure Pressure - force acting on an object per unit area.

Chapter 124 Pressure -Conversion Factors -1 atm (atmosphere) = 760 mmHg -1 atm (atmosphere) = 760 torr -1 atm (atmosphere) =  10 5 Pa (Pascal) -1 atm (atmosphere) = kPa (Kilopascal)

Chapter 125 The Gas Laws -There are four variables required to describe a gas: -Amount of substance: moles -Volume of substance: liters -Pressures of substance: atmospheres (atm) -Temperature of substance: kelvin -The gas laws will hold two of the quantities constant and see how the other two vary.

Chapter 126 The Gas Laws The Pressures-Volume Relationship: Boyle’s Law Boyle’s Law - The volume of a fixed quantity of gas is inversely proportional to its pressure at constant temperature.

Chapter 127 The Gas Laws The Pressures-Volume Relationship: Boyle’s Law Boyle’s Law - The volume of a fixed quantity of gas is inversely proportional to its pressure at constant temperature.

Chapter 128 The Gas Laws The Temperature-Volume Relationship: Charles’s Law Charles’s Law - The volume of a fixed quantity of gas at constant pressure is directly proportional to the substances temperature in Kelvin.

Chapter 129 The Gas Laws The Temperature-Volume Relationship: Charles’s Law Charles’s Law - The volume of a fixed quantity of gas at constant pressure is directly proportional to the substances temperature in Kelvin.

Chapter 1210 The Gas Laws The General Gas Law - This is a combination of Boyle’s and Charles’s gas law.

Chapter 1211 The Gas Laws The Quantity-Volume Relationship: Avogadro’s Law Avogadro’s Law - The volume of gas at a given temperature and pressure is directly proportional to the number of moles of gas.

Chapter 1212 The Ideal Gas Equation -Combine the gas laws (Boyle, Charles, Avogadro) yields a new law or equation. Ideal gas equation: PV = nRT R = gas constant = L(atm)/mol(K) P = pressure (atm)V = volume (L) n = molesT = temperature (K)

Chapter 1213 The Ideal Gas Equation -We define STP (standard temperature and pressure) as 0  C ( K), 1 atm. -Volume of 1 mol of gas at STP is 22.4 L (molar vol.).

Chapter 1214 Gas Densities and Molar Mass -Rearranging the ideal-gas equation with M as molar mass yields Applications of The Ideal-Gas Equation

Chapter 1215 Gas Mixtures and Partial Pressures Dalton’s Law - In a gas mixture the total pressure is given by the sum of partial pressures of each component: P total = P 1 + P 2 + P 3 + … - The pressure due to an individual gas is called a partial pressure.

Chapter 1216 Gas Mixtures and Partial Pressures Partial Pressures and Mole Fractions -The partial pressure of a gas can determined if you know the mole fraction of the gas of interest and the total pressure of the system. -  i is the mole fraction of gas i (n i /n total ). P i =  i P total

Chapter 1217 Kinetic-Molecular Theory -Theory developed to explain gas behavior -To describe the behavior of a gas, we must first describe what a gas is: –Gases consist of a large number of molecules in constant random motion. –Volume of individual molecules negligible compared to volume of container. –Intermolecular forces (forces between gas molecules) negligible. –Energy can be transferred between molecules, but total kinetic energy is constant at constant temperature. –Average kinetic energy of molecules is proportional to temperature.

Chapter 1218 Molecular Effusion and Diffusion Graham’s Law of Effusion Graham’s Law of Effusion - The rate of effusion of a gas is inversely proportional to the square root of its molecular weight. -Effusion is the escape of a gas through a tiny hole (a balloon will deflate over time due to effusion).

Chapter 1219 Real Gases: Deviations from Ideal Behavior -The assumptions in kinetic molecular theory show where ideal gas behavior breaks down –When the volume of the gas becomes very small (the volume of the gas molecules become significant) –When the pressure become very large (gas molecules start to attract each other).

Chapter 1220 Real Gases: Deviations from Ideal Behavior

Chapter 1221 Real Gases: Deviations from Ideal Behavior The van der Waals Equation We add two terms to the ideal gas equation one to correct for volume of molecules and the other to correct for intermolecular attractions The correction terms generate the van der Waals equation: where a and b are empirical constants.

Chapter , 14, 20, 28, 36, 38, 48, 56 Homework