An aluminum kettle weighing 1.2 kg contains 2 kg of water at a temperature of 15 degrees.

An aluminum kettle weighing 1.2 kg contains 2 kg of water at a temperature of 15 degrees. How much kerosene does it take to boil water?

mh = 1.2 kg.
Ca = 920 J / kg * ° C.
mw = 2 kg.
Cw = 4200 J / kg * ° C.
t1 = 15 ° C.
t2 = 100 ° C.
q = 4.6 * 107 J / kg.
mk -?
The boiling point of water is t2 = 100 ° C. Since the water is in the aluminum kettle, the amount of heat Qc, which is released during the combustion of kerosene, is used to heat not only the water Qw, but also the kettle Qh: Qc = Qw + Qh.
Qk = q * mk.
Qw = Cw * mw * (t2 – t1).
Qh = Ca * mh * (t2 – t1).
q * mk = Cw * mw * (t2 – t1) + Ca * mh * (t2 – t1).
mk = ((Cw * mw + Ca * mh) * (t2 – t1)) / q.
mk = ((4200 J / kg * ° C * 2 kg + 920 J / kg * ° C * 1.2 kg) * (100 ° C – 15 ° C)) / 4.6 * 107 J / kg = 0 , 02 kg.
Answer: in order to heat the water in a kettle to a boil, it is necessary to burn mk = 0.02 kg of kerosene.