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NEET CHEMISTRYMedium

An engine operating between 150°C and 25°C takes 500 J heat from a higher temperature reservoir. If there are no frictional losses, then the work done by the engine is [MH CET 1999]:

A

147.7 J

B

157.75 J

C

165.85 J

D

169.95 J

Step-by-Step Solution

To find the work done by an ideal heat engine (Carnot engine) operating between two temperatures, we first convert the temperatures to the Kelvin scale:

  1. Thigh=150+273.15=423.15T_{high} = 150 + 273.15 = 423.15 K .
  2. Tlow=25+273.15=298.15T_{low} = 25 + 273.15 = 298.15 K .

The efficiency (ηη) of an ideal engine with no frictional losses is determined by the temperature of the reservoirs: η=1(Tlow/Thigh)=(ThighTlow)/Thighη = 1 - (T_{low} / T_{high}) = (T_{high} - T_{low}) / T_{high}.

Substituting the values: η=(423.15298.15)/423.15=125/423.150.2954η = (423.15 - 298.15) / 423.15 = 125 / 423.15 ≈ 0.2954.

The efficiency is also the ratio of work done (WW) to the heat taken from the higher temperature reservoir (QhighQ_{high}): η=W/Qhighη = W / Q_{high}.

Rearranging to find work: W=Qhigh×ηW = Q_{high} \times η W=500 J×0.2954147.7 JW = 500\text{ J} \times 0.2954 ≈ 147.7\text{ J}.

Thus, the work done by the engine is approximately 147.7 J, matching Option A.

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