Presentation on theme: "Chapter 5 Gases. 2 Early Experiments Torricelli performed experiments that showed that air in the atmosphere exert pressure. Torricelli designed the first."— Presentation transcript:
10 Avogadro’s Law : V=an A gas at constant temperature and pressure the volume is directly proportional to the number of moles of gas.
11 Ideal Gas Law Equation of state for a gas PV=nRT P: atm V: Liter n: moles R: 0.082 L atm K -1 T: K
12 Laws for Gas experiments Boyle’s Law : PV=k Charles’s Law : V=bT Avogadro’s Law : V=an The ideal Gas Law : PV=nRT (so called equation of state for idea gas)
13 Ideal Gas The volume of the individual particles can be assumed to be negligible. The particles are assumed to exert no force on each other. It expresses behavior that real gases approach at low pressure and high temperature.
14 Gas Stoichiometry Standard Temperature and Pressure (STP) T=0 o C P=1 atm V=22.4 L Natural Temperature and Pressure (NTP) T=25 o C P=1 atm V=24.5L
20 The Model of Ideal Gas in Kinetic- Molecular Theory The volume of the individual particles can be assumed to be negligible. The particles are assumed to exert no force on each other. The particles are in constant motion. The average kinetic energy of a collection of gas particles is assumed to be directly proportional to the Kelvin temperature of the gas.
21 An ideal gas particle in a cube wholse sides are of length L (in meters).
22 The velocity u can be broken down into three perpendicular components, u x, u y, and u 2.
23 Pressure of an Ideal Gas Let the container be a rectangular box with sides of length L x, L y and L z. Let v be the velocity of a given molecule.
24 In the xy plane, v x 2 + v y 2 = v yx 2 by the Pythagorean theorem.
31 Distribution of Molecular Speeds in an Ideal Gas Root mean square speed is assumed that all molecules move at the same speed. The motions of gas molecules should have distribution of molecular speeds in equilibrium.
43 Definition of Pressure The pressure of a gas results from collisions between the gas particles and the walls of the container. Each time a gas particle hits the wall, it exerts a force on the wall. An increase in the number of gas particles in the container increases the frequency of collisions with the walls and therefore the pressure of the gas.
44 The effusion of a gas into an evacuated chamber.
45 Suppose there is a tiny hole of area A in the wall and that outside the container is a vacuum. Escape of a gas through a tiny hole is called effusion. collisions × area
46 Diffusion Relative diffusion rates of NH 3 and HCl molecules
47 Molecules Collisions and Mean Free Path Intermolecular collisions are important in reaction kinetics. Assume a molecule as a hard sphere. No intermolecular forces exist except at the moment of collision. z AA : the number of collisions per unit time that one particular A molecule makes with other A molecule [collisions s -1 ]
64 Calculate pressure for 1 mole of CO 2 at 0 o C in containers with 22.4 L P = 0.995 atm Use idea gas equation Use van der Waals equation
65 Calculate pressure for 1 mole of CO 2 at 0 o C in containers with 0.2 L Use idea gas equation Use van der Waals equation P = 52.6 atm
66 Calculate pressure for 1 mole of CO 2 at 0 o C in containers with 0.05 L Use idea gas equation Use van der Waals equation P = 1620 atm
67 Analysis of the van der Waals Constants~a constant The a constant corrects for the force of attraction between gas particles. attraction between particles↑ a ↑ As the force of attraction between gas particles becomes stronger, we have to go to higher temperatures for the molecules in the liquid to form a gas. Gases with very small values of a, such as H 2 and He, must be cooled to almost absolute zero before they condense to form a liquid.
68 Analysis of the van der Waals Constants~b constant a rough measure of the size of a gas particle the volume of a mole of Ar atoms is 0.03219 L r = 2.3 x 10 -8 cm