A heat engine operates on a Carnot cycle that runs clockwise between a reservoir at 340 K and a reservoir at 280 K. One cycle moves enough energy from the high-temperature reservoir to raise the temperature of 1.0 kg of water by 1.0 K. How much work is done by the engine in one cycle

Respuesta :

Answer:

w = 736 J

Explanation:

A Carnot cycle is a theoretical thermodynamic cycle that establishes the maximum efficiency of a heat engine operating between two heat sources at different temperatures.

The efficiency of a thermal engine is how much of the heat from the hot reservoir it can transform into work.

[tex]\eta = \frac{w}{q1}[/tex]

Where:

η: efficiency

w: work

q1: heat taken from the hot source

Therefore, the work can be calculated as:

[tex]w = \eta * q1[/tex]

We know the heat energy taken from the hot reservoir is the energy needed to raise the temperature of 1 kg of water in 1 K.

This is the definition of one Kcal.

q1 = 1 kcal

The efficiency of the Carnot cycle is determined by the temperatures of the reservoirs.

[tex]\eta = 1 - \frac{T2}{T1}[/tex]

These temperatures must be expressed in an absolute temperature scale (such as degrees Kelvin or degrees Rankine)

So in this case the work per cycle is:

[tex]w = q1 * (1-\frac{T2}{T1} )[/tex]

[tex]w = 1 kcal * (1-\frac{280 K}{340 K} ) = 0.176 kcal[/tex]

Now, work is not usually expressed in calories, so it should be converted to Joules:

1 kcal = 4184 J

[tex]w = 0.176 kcal * \frac{4184 J}{1 kcal} = 736 J[/tex]

The work done by the engine will be "736 J".

Heat engine

According to the question,

Mass, m = 1.0 kg

Temperature, T₁ = 280 K

                       T₂ = 340 K

Heat taken from source, q₁ = 1 Kcal

We know the relation, efficiency of thermal engine be:

→ η = [tex]\frac{w}{q_1}[/tex]

  w = η × q₁

here,

   η = 1 - [tex]\frac{T_2}{T_1}[/tex]

now,

→ w = q₁ × (1 - [tex]\frac{T_2}{T_1}[/tex])

By substituting the values, we get

      = 1 × (1 - [tex]\frac{280}{340}[/tex])

      = 0.176 kcal

Thus the above answer is appropriate.  

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