Energy

Energy is an inherent property of a system. Any system at a given set of conditions (e.g. pressure and temperature) has a certain energy content. The concept of energy invented to describe a number of processes such as conversion of work to heat. The SI unit of energy is joule (J). Other units are:

1 cal (calorie)= 4.1868 J
1 kcal= 4186.8 J
1 Btu (British thermal unit)= 1055.05 J
1 thermie= 4.184E6 J
1 ft.lbf= 1.35582 J
1 kJ= 1000 J
1 MJ= 1E6 J
1 hp.h (horsepower.hour)= 2.6845E6 J
1 kWh= 3.6E6 J
1 MWh= 3.6E9 J
1 eV (electron volt)= 0.16021E-18 J
1 erg= 1E-7 J
Related topic:

The first law of thermodynamics