Water weighing 0.3 kg was heated in an alcohol lamp from 20 degrees to 80 degrees and 7 g

Water weighing 0.3 kg was heated in an alcohol lamp from 20 degrees to 80 degrees and 7 g of alcohol was burned. Determine the efficiency of the spirit lamp.

Data: m1 (mass of water heated on an alcohol lamp) = 0.3 kg; t0 (initial temperature) = 20 ºС; t (final temperature) = 80 ºС; m2 (mass of alcohol burned) = 7 g (7 * 10 ^ -3 kg).

Reference values: Sv (specific heat of water) = 4200 J / (kg * K); q (specific heat of combustion of alcohol) = 2.7 * 10 ^ 7 J / kg.

The efficiency of the taken spirit lamp is calculated by the formula: η = Qp / Qz = Sv * m1 * (t – t0) / (q * m2).

Calculation: η = 4200 * 0.3 * (80 – 20) / (2.7 * 10 ^ 7 * 7 * 10-3) = 0.4 (40%).

Answer: The efficiency of the spirit lamp is 40%.