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

| June 20, 2021 | education

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

mw = 0.3 kg.

t1 = 20 ° C.

t2 = 80 ° C.

C = 4200 J / kg * ° C.

q = 2.7 * 107 J / kg.

mс = 7 g = 0.007 kg.

Efficiency -?

The coefficient of efficiency The efficiency of the spirit lamp shows what part of the consumed thermal energy Qs, expressed as a percentage, goes into useful work Qp: Efficiency = Qp * 100% / Qz.

The consumed heat Qz is the heat energy that is released during the combustion of alcohol.

Qz = q * mc.

Qz = 2.7 * 107 J / kg * 0.007 kg = 189000 J.

Useful thermal energy Qp is the energy that goes to heat water.

Qp = C * mw * (t2 – t1).

Qp = 4200 J / kg * ° C * 0.3 kg * (80 ° C – 20 ° C) = 75600 J.

Efficiency = 75600 J * 100% / 189000 J = 40%.

Answer: an alcohol lamp has an efficiency of 40%.



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