Chemistry - Chapter 10: Gas Laws

gas

a substance that has no well-defined boundaries but diffuses rapidly to fill any container in which it is placed in

e.g. NH3 and HCl - diffuse towards each other (high concentration to area of low concentration)

properties of gases

• diffuses quickly

• can be compressed

• no fixed shape/volume

• low density

• increased pressure → volume decreases

• increased temperature → increased volume

• decreased temperature → decreased volume

temperature

uses Kelvin (273K)

pressure

the force that the gas exerts on each unit of area of its container unit

Pascals (Pa/kPa for kilopascals) or Newtons per metre squared (Nm-²)

volume

volume of a sample of gas is the same as the volume of the container in which it is held

*remember:

1L = 1000cm³

1m³ = 100cm³

Boyle’s Law

at constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure

therefore, the higher the pressure, the lower the volume

Charles’ Law

the volume of a fixed mass of gas is directly proportional to its temperature measured on the Kelvin scale, provided that the pressure remains the same

combined formula of Boyle and Charles

P1V1/T1 = P2V2/T2

Gay-Lussac’s Law of Combining Volumes

in a reaction between gases, the volumes of the reacting gases and the gaseous products are in the role of small whole numbers (provided volumes are measured at the same temperature and pressure)

so the pressure of a gas increases as its temperature increases

Avogadro’s law

equal volumes of gases contain equal numbers of molecules (under same conditions of temperature and pressure)

assumptions of the kinetic theory of gases

• gases are made up of particles in continuous rapid random motion

• the kinetic energy of particles in a gas is proportional to the temperature

• there are no attractive or repulsive forces between the molecules

• the volume of molecules is negligible compared to the space that they occupy

• there is no loss of kinetic energy in collisions

limitations

• intermolecular forces exist between molecules in a gas

• under high pressure, the volume of a gas is not negligible compared to the space it occupies

there, the kinetic theory don’t hold for real gases, but only ideal gases

ideal gases

gases that obey all the assumptions of the kinetic theory of gases under all conditions of temperature and pressure

real gases

differ from ideal gases due to incorrect statements of:

(i) forces of attraction and repulsion do not exist between molecules

(ii) the volume of molecules is not negligible

at s.t.p

100 kPa pressure

22.4L volume

273K temperature

the equation for state of any ideal gas (pg 64 of logsform book)

pV = nRT

• p = pascals

• v = m³

• n = number of moles

• r = 8.31J mol^-1 K^-1 = gas constant

• t = kelvin