How much alcohol needs to be burned to heat 500 g of water from 20 ° to 80 ° C? The heat of combustion of alcohol

How much alcohol needs to be burned to heat 500 g of water from 20 ° to 80 ° C? The heat of combustion of alcohol is 26 MJ / kg, the heat capacity of water is 4200 J / (kg • ° С)

Initial data: m1 (mass of water) = 500 g or 0.5 kg; t0 (water temperature before heating) = 20 ºС; t (final water temperature) = 80 ºС.

Reference data: according to the condition q (specific heat of combustion of alcohol) = 26 MJ / kg or 26 * 10 ^ 6 J / kg; C (specific heat of water) = 4200 J / (kg * ºС).

To determine the mass of alcohol, we assume that there are no heat losses during its combustion.

Q1 = Q2: C * m1 * (t – t0) = q * m2.

m2 = C * m1 * (t – t0) / q = 4200 * 0.5 * (80 – 20) / (26 * 10 ^ 6) = 0.00485 kg or 4.85 g.