How many grams of alcohol do you need to burn in an alcohol lamp to heat 580 g water at 80 ° C on it?

| November 16, 2020 | education

How many grams of alcohol do you need to burn in an alcohol lamp to heat 580 g water at 80 ° C on it? The efficiency of the spirit lamp is 20%. (specific heat of combustion of alcohol 2.9 ∙ 107 J / kg, specific heat of water 4200 J / kg ∙ 0С)

mw = 580 g = 0.58 kg.
Δt = 80 “C.
Efficiency = 20%.
λ = 2.9 * 10 ^ 7 J / kg.
C = 4200 J / kg * “C.
mс -?
decision
Let us find the amount of heat Qv required for heating water: Qw = C * mw * Δt.
Let’s write down the definition for the efficiency of the spirit lamp: efficiency = Qw * 100% / Qs.
Let us express the amount of heat Qс, which is released during the combustion of alcohol: Qс = λ * mс.
Efficiency = C * mw * Δt * 100% / λ * ms.
mc = C * mw * Δt * 100% / λ * efficiency.
mс = 4200 J / kg * “C * 0.58 kg * 80” C * 100% / 2.9 * 10 ^ 7 J / kg * 20% = 0.0336 kg = 33.6 g.
Answer: to heat the water, it is necessary to burn mс = 33.6 g of alcohol.



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