What are some common mistakes students make with the Gay Lussac's law?
Not converting the temperatures to absolute zero Kelvin scale.
Pressure is directly related to absolute temperature. So an increase from 20 degrees K to 40 degrees K doubles the pressure. But an increase from 20 degrees C to 40 degrees C does not. The most common mistakes is not converting the temperature to the Kelvin Scale where temperature and pressure are directly related.