How many BTU's will it take to melt 2 tons of ice in 2 hours?
The enthalpy of fusion of water is 333.55 kJ/kg. One metric ton equals 1000 kg, so melting 2 tons of ice would take 2000kg * 333.55kJ/kg = 6.671*10^8 J
One BTU = 1.055*10^3 J, so melting 1 metric ton of ice would take:
(6.671*10^8 J)/(1.055*10^3 J/BTU) = 6.323*10^5 BTU
It does not matter how much time it takes to melt the ice. A BTU is a unit of energy, not power, and it takes the same amount of energy regardless of how long it takes.
To melt the ice in two hours, though, one would need to add energy to the ice at a rate of (6.671*10^8 J)/(2hr) = 9.265*10^4 W. Watts are the SI unit of power, which is energy per unit time.
