Temperature Scales
- On the thermodynamic (Kelvin) temperature scale, absolute zero refers to the lowest possible temperature
- This is equal to 0 K or −273 °C
- It is not possible to have a temperature lower than 0 K
- This means a temperature in Kelvin will never be a negative value
- Absolute zero is defined as:
The temperature at which the molecules in a substance have zero kinetic energy
- This means for a system at 0 K, it is not possible to remove any more energy from it
- Even in space, the temperature is roughly 2.7 K, just above absolute zero
How to use the Kelvin Scale
- To convert between temperatures θ in the Celsius scale, and T in the Kelvin scale, use the following conversion:
θ / °C = T / K − 273
T / K = θ / °C + 273
Conversion chart between temperature scales in Kelvin and Celsius
- The divisions on both scales are equal, which means
A change in a temperature of 1 K is equal to a change in temperature of 1 °C
Worked example
In many ideal gas problems, room temperature is considered to be 300 K.
What is this temperature in degrees Celsius?
Answer:
Step 1: Recall the Kelvin to Celsius conversion
θ / °C = T / K − 273
Step 2: Substitute in the value of 300 K
300 K − 273 = 27 °C
Examiner Tip
If you forget in the exam whether it’s + or −273, check the data booklet!
Temperature (K) = temperature (°C) + 273
This helpful reminder is there under 'unit conversions'
