The energy density of coal can also be expressed in kilowatt-hours for some unit of mass, the units that electricity is most commonly sold in, to estimate how much coal is required to power...
1 kilocalorie = 4186.8 joules, and 1 joule/sec = 1 watt. So 1 kwh = 1000 x 3600 watt.secs = 3.6 x 106 joules. So answer = 4186.8/(3.6 x 106) = 1.163 x 10-3 kwh. This could also be expressed as 4.2...