To convert a temperature from Celsius to Kelvin, we add 273.15, which is the value representing absolute zero in the Kelvin scale. The Kelvin scale starts at absolute zero, where molecular motion stops, making it the lowest possible temperature. This value of 273.15 corresponds to 0 degrees Celsius, which is the freezing point of water.
For scientific calculations, we often round this value to 273 for simplicity. Therefore, when we add 273 to a Celsius temperature, we are effectively shifting the starting point of our temperature scale from 0 degrees Celsius to the absolute zero point in Kelvin. This is crucial in scientific contexts where temperatures need to be expressed in Kelvin for various equations and laws, such as gas laws and thermodynamics.