• Properties of Gases
• A gas is defined as a substance that has no well- defined boundaries, but
diffuses rapidly to fill any container in which it is placed.
– No definite shape
– No definite volume
– Can flow
– Can be compressed
• Boyles law
• At a constant temperature, the volume of a fixed mass of gas is inversely
proportional to its pressure
•
V ɚ 1/P
• Graph of P Vs 1/V
• PV = k
• Charles law
• At a constant pressure, the volume of a fixed mass of gas is directly
proportional to its temperature measured on the Kelvin scale
• V ɚ T
• V = kT
V/T = k
• Combined laws
• P1V1 = P2V2 and V1/T1 = V2/T2
• P1V1/T1 = P2V2/T2
• T must be in Kelvin
• Kinetic theory of gases
• Gases consist of tiny particles in continuous motion
• There are no attractive or repulsive forces between molecules
• Volume of molecules are negligible compared to volume of container
• All collisions are perfectly elastic
• Average kinetic energy of the molecules are proportional to the
temperature (on Kelvin scale)
• Ideal gases
• Ideal gas obeys all these conditions at all pressures and temperatures.
• No such gas exists
• Gases come closest to this at low pressure and high temperatures
• Equation of ideal gas: PV = nRT
• P = pressure in pascals
• V = volume in m³
• n = number of moles
• R = universal gas constant (always given)
• T = temperature in Kelvin