Properties of Gases Kinetic-Molecular Theory Based on particle motion 1. Gas particles are tiny compared to the great distances between them ◦ O 2 molecules travel 20,000 times diameter between collisions (6’ diameter – 22.7 miles) 2. Travel constantly, at extremely high velocity in all directions at many different speeds ◦ Collisions constantly change their speed and direction

Properties of Gases 3. Particles do not interact with each other or the walls of their container except during momentary collisions. ◦ Chemical, gravitational, electrical forces can be ignored. Many collisions - 5,000,000,000/second at 0C. 4. Collisions between particles are elastic Collisions between particles are elastic ◦ Net kinetic energy unchanged 5. Average kinetic energy directly proportional to temp of gas in K ◦ As temp rises, particles move faster, collide more

Physical Properties of Gases Diffusion – gases fill entire volume of container over time Effusion – gas particles pass thru tiny opening into an evacuated space ◦ Graham’s law of effusion ◦ R = 1 √Molar mass

Physical Properties of Gases Permeability ◦ Gas can pass thru another porous substance  Why balloons go flat and your lungs work Fluidity ◦ Can flow and take shape of container  Why there is wind Compressibility and expansibility

Physical Properties of Gases Pressure – caused by the force of billions of collisions on a boundary ◦ No boundary – no pressure ◦ There is gas in space – but there is no boundary Measure – force per unit area ◦ Inside a balloon – many billions of collisions per second ◦ Pressure always perpendicular to the surface

Physical Properties of Gases Measures of pressure ◦ PSI – force (lbs) per unit area (in 2 ) ◦ Millimeters of mercury or torr  How high atmospheric pressure causes mercury to rise in a column ◦ Atmosphere – 1 Atm = normal atmospheric pressure at sea level at latitude 45  2.0= double, 0.5 = ½

Physical Properties of Gases Measures of pressure ◦ SI unit – Pascal  Force of one Newton acting on one square meter Conversion factors 1atm 1atm 760 torr 1 atm 760 torr 14.7 psi 14.7psi 101,325 Pa

Physical Properties of Gases Pressure, Volume and Temperature ◦ Pressure up, volume down (inverse) temp same ◦ Temp up, volume up—down, volume down ◦ Volume same, temp increase – pressure increase  Temp down – pressure down  PRESSURE PRESSURE

Gas Laws and Formulas Boyle’s Law – Pressure and Volumes Boyle’s Law ◦ The volume of a gas is inversely realted to the pressure if the temperature is held constant.  PV = k  P = pressure, V = volume, k = a constant  So, P 1 V 1 = k = P 2 V 2  For any value of P, V will relate such that k remains constant and vice versa

Gas Laws and Formulas Charles’ Law– Temperature and Volumes Charles’ Law ◦ When the pressure on a sample of a dry gas is held constant, the Kelvin temperature and the volume are directly related.  V = k T  T = Temperature V = volume, k = a constant  So, V 1 = k = V 2 ◦ T 1 T 2 ◦ As V increases or decreases, T must do the same so that k will remain constant

Gas Laws and Formulas Gay-Lussac’s Law Temperature and Pressures ◦ Pressure is directly proportional to temperature in kelvins for a fixed mass of gas held in a constant volume.  P = k T  T = Temperature P = Pressure, k = a constant  So, P 1 = k = P 2 ◦ T 1 T 2 ◦ As P increases or decreases, T must do the same so that k will remain constant

Gas Laws and Formulas Combined Gas Law ◦ Boyle’s, Charles, and Gay-Lussac’s require something to be constant.  Boyle’s – temperature  Charles – pressure  Gay-Lussac – mass and volume ◦ What to do when things aren’t constant?  Combined gas law  Combination equation taking into account all three variables  PV = k  T

Gas Laws and Formulas Dalton’s Law of Partial Pressures ◦ Gases are seldom pure, there are always contaminants ◦ The total pressure of a mixture of gases equals the sum of the partial pressures  P total = P 1 +P 2 +P 3 +P……..  Gas collection over water introduces water vapor  Pressure will equal gas collected plus vapor pressure of water at temperature collected  Since it is collected over water and displaces the water under 1atm, total pressure is always atmospheric pressure at your location (see barometer)