Page USEFUL DATA atmosphere atmos press at sea level 0.3 m water or 6 mm mercury or 01. kPa mm mercury .13 kPa litre fresh water kg m fresh water 00 kg tonne t m 00 litre 0 kPa 0.1 m head of water m head of water .8 kPa mm head of water .8 Pa Work done in joules force in Newtons × distance in metres or J Nm Power in watts work in joules done per second or W J/s Nm/s Power W force N × velocity m/s kg steam Latent heat of steam from and at 0 C 25 kJ Latent heat of fusion of ice 3 kJ/kg tonne of refrigeration 3 × 00 3500 kJ tonne of refrigeration h  3500 395 kJ h 3 kJ min Temperature Scales Freezing point of water C 7 K Boiling point of water 0 C 7 K One degree Celsius one Kelvin