6.2.3

# Ideal Gases

Test yourself

## The Kelvin Scale

The Kelvin scale is a temperature scale that is commonly used in science.

### The Kelvin scale

• The Kelvin scale is an absolute temperature scale defined to have 0 K at the lowest possible temperature, called absolute zero.

### Absolute zero

• Absolute zero (0 K) is the lowest possible temperature.
• At absolute zero, there is no temperature.
• This means that there is no kinetic energy or vibration of molecules.

### Converting from degrees Celsius to Kelvin

• To find degrees Celsius from Kelvin, just add 273.15.
• E.g. 0oC = 273.15 K.
• E.g. Water boils at 373.15 K.

## Ideal Gas Law

The ideal gas law is a good model for the behaviours of large amounts of gas.

### Ideal gas law

• The ideal gas law can be written as:
• Pressure x volume = number of moles x ideal gas constant x temperature
• pV=nRT
• Where R is the ideal gas constant and has a value of 8.31
• This equation can be rearranged to solve for any of the terms.

### Boltzmann constant

• Ideal gas constant x number of moles = Boltzmann constant x number of molecules
• $Rn=kN$

• This equation gives the relationship between the ideal gas constant, the Boltzmann constant and Avogadro's number (the number of molecules in a mole):
• $N{_a}=R/k$
• Using the ideal gas law and the above equation, we can now write:
• $pV=NkT$