Find the efficiency of a primus in which 50 g of kerosene burned out when 4 liters of water

Find the efficiency of a primus in which 50 g of kerosene burned out when 4 liters of water were heated from 20 to 75 degrees.

Initial data: m1 (mass of heated water) = 4 kg (V = 4 l); t0 (initial water temperature) = 20 ºС; t1 (final water temperature) = 75 ºС; m2 (mass of burned kerosene) = 50 g = 0.05 kg.

Constants: C (specific heat capacity of water) = 4200 J / (kg * K); q (specific heat of combustion of kerosene) = 46 * 10 ^ 6 J / kg.

The efficiency of the primus is calculated from the following formula:

η = Qп / Q3 = С * m1 * (t1 – t0) / (q * m2) = 4200 * 4 * (75 – 20) / (46 * 10 ^ 6 * 0.05) ≈ 0.4 or 40% …

Answer: The efficiency of the primus is 0.4 or 40%.