# What mass of water can be heated from 20 C to the boiling point on a lamp in which 200 g

**What mass of water can be heated from 20 C to the boiling point on a lamp in which 200 g of kerosene burns, and its efficiency is 12%?**

t1 = 20 ° C.

t2 = 100 ° C.

mk = 200 g = 0.2 kg.

C = 4200 J / kg * ° C.

λ = 4.6 * 10 ^ 7 J / kg.

Efficiency = 12%.

mv -?

When kerosene is burned, the amount of thermal energy Qk is released in the lamp: Qk = λ * mk, where λ is the specific heat of combustion of kerosene, mk is the mass of kerosene that has burned.

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

Since water is heated to boiling point, t2 = 100 ° C.

But since only 12% of the heat released during combustion goes to heating the water, then Qc * efficiency / 100% = Qw.

λ * mk * efficiency / 100% = C * mw * (t2 – t1).

mv = λ * mk * efficiency / 100% * C * (t2 – t1).

mw = 4.6 * 10 ^ 7 J / kg * 0.2 kg * 12% / 100% * 4200 J / kg * ° * (100 ° C – 20 ° C) = 3.3 kg.

Answer: on a kerosene lamp, you can heat up to the boiling point mw = 3.3 kg of water.