Gas Laws Section 3.2

Boyle’s Law At a constant temperature, the volume of a given mass of any gas is inversely proportional to the pressure of the gas. http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/gaslaw/boyles_law_graph_new.swf

Charles’ Law At a constant pressure, the volume of a given mass of any gas is directly proportional to the Kelvin Temperature. http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/gaslaw/charles_law.swf

Gay – Lussac’s Law of Combining Volumes When a gases react, the volumes consumed in the reaction bear a simple whole number ratio to each other, and to the volumes of any gaseous product of the reaction, if all volumes are measured under the same conditions of temperature and pressure.

Avogadro’s Law Equal volumes of (ideal) gases, contain the same number of particles, or molecules, under the same conditions.

All the Law’s Combined Charles’ Law Boyle’s Law Ideal Gas Law PV = nRT Combined Gas Law

The Combined Gas Laws Combined Gas Law P1, V1, and T1 are the initial pressure, volume and Kelvin temperature. P2, V2 and T2 are the final pressure, volume and Kelvin temperature. Pressure can be in any units as long as it’s the same for P1 and P2. Volume can be in any units as long as it’s the same for V1 and V2. Temperature must be in Kelvin’s for T1 and T2. To convert from degrees to Kelvin’s add on 273. For example 25o = 25 + 273 = 298 K

Temperature must be in Kelvin’s

S.T.P. (Standard, Temperature and Pressure) Scientists who first studied gases soon realised that the pressure and temperature controlled the volume observed for a gas sample. Therefore to compare different gas samples, they defined a set of reference conditions. These conditions are known as standard, temperature and pressure, or simply STP, and are 273 K, and 101,325 Pa.

The Kinetic Theory of Gases The kinetic theory of gases was developed by James Clerk Maxwell and Ludwig Boltzmann. This theory assumes that: Gases are made up of particles whose diameters are negligible compared to the distances between them. There are no attractive or repulsive forces between these particles. The particles are in constant rapid random motion, colliding with each other and with the walls of the container. The average kinetic energy of the particles is proportional to the Kelvin temperature. All collisions are perfectly elastic .

Ideal Gases versus Real Gases An ideal gas is one which obeys all the gas laws and under all conditions of temperature and pressure. No such gases exists, but real gases behave most like an ideal gas at high temperatures and at low pressures. Under these conditions, the particles of a real gas are relatively far away from each other, and the assumptions of the kinetic theory are reasonably valid.

Why do real gases deviate? Intermolecular forces are present. (Such as dipole – dipole, Van der Waals, etc.,) Molecules have volume. Collisions are not perfectly elastic.

Equation of State for an Ideal Gas