How much peat needs to be burned to heat 3 kg of water at 20 ° C to a boil

How much peat needs to be burned to heat 3 kg of water at 20 ° C to a boil. specific heat of combustion of peat 15MJ / kg, specific heat of water 4200J / Kg × ° С

mw = 3 kg.

t1 = 20 ° C.

t2 = 100 ° C

C = 4200 J / kg * ° C.

q = 15 MJ / kg = 15 * 10 ^ 7 J / kg.

mt -?

The amount of heat Q required for heating water is determined by the formula: Q = C * mw * (t2 – t1), where C is the specific heat capacity of water, mw is the mass of water, t1, t2 are the initial and final water temperatures.

The amount of heat Q, which is released during the combustion of fuel, is determined by the formula: Q = q * mt, where q is the specific heat of combustion of the fuel, mt is the mass of the substance that burned.

C * mw * (t2 – t1) = q * mt.

mt = C * mw * (t2 – t1) / q.

mt = 4200 J / kg * ° C * 3 kg * (100 ° C – 20 ° C) / 15 * 10 ^ 7 J / kg = 0.00672 kg.

Answer: to heat the water, it is necessary to burn mt = 0.00672 kg of peat.