How many kilograms of dry firewood do you need to burn to heat 10kg of water from 30 C to a boil.

To calculate the mass of consumed dry firewood, we use the equality: qd * md = Q = Sv * mw * (tboil – t0), whence md = Sv * mw * (tboil – t0) / qd.

Constants and variables: Sv – heat capacity of water (Sv = 4200 J / (kg * K)); mw is the mass of heated water (mw = 10 kg); tboil – temperature of the beginning of boiling (tboil = 100 ºС); t0 – initial temperature (t0 = 30 ºС); qd is the heat of combustion of dry firewood (qd = 1 * 10 ^ 7 J / kg).

Calculation: md = Sv * mw * (tboil – t0) / qd = 4200 * 10 * (100 – 30) / (1 * 10 ^ 7) = 0.294 kg.