An ice-making machine inside a refrigerator operates in a Carnot cycle. It takes heat from liquid water at 0.0 ∘C and rejects heat to a room at a temperature of 22.5 ∘C. Suppose that liquid water with a mass of 85.7 kg at 0.0 ∘C is converted to ice at the same temperature. Take the heat of fusion for water to be Lf = 3.34×105 J/kg .How much energy E must be supplied to the device?

Respuesta :

Answer:

2.36 x 10^6 J

Explanation:

Tc = 0°C = 273 K

TH = 22.5°C = 295.5 K

Qc = heat used to melt the ice

mass of ice, m = 85.7 Kg

Latent heat of fusion, L = 3.34 x 10^5 J/kg

Let Energy supplied is E which is equal to the work done

Qc = m x L = 85.7 x 3.34 x 10^5 =  286.24 x 10^5 J

Use the Carnot's equation

[tex]\frac{Q_{H}}{Q_{c}}=\frac{T_{H}}{T_{c}}[/tex]

[tex]Q_{H}=286.24\times 10^{5}\times \frac{295.5}{273}[/tex]

QH = 309.8 x 10^5 J

W = QH - Qc

W = (309.8 - 286.24) x 10^5

W = 23.56 x 10^5 J

W = 2.36 x 10^6 J

Thus, the energy supplied is 2.36 x 10^6 J.

The amount of energy that must be supplied to the device is calculated using the opposite principle of a heat engine. The value obtained is 2,359,104.39 J.

Refrigerator and Carnot Engine

Given that cooler temperature is,

[tex]T_1=0^\circ \,C = 273\,K[/tex]

The hotter temperature is;

[tex]T_2=22.5^\circ \,C = 295.5\,K[/tex]

The heat used to melt a certain mass of water can be given as;

[tex]Q_1 = m\times L_f[/tex]

Substituting the known values, we get;

[tex]Q_1 = 85.7\,kg \times 3.34\times 10^5\,J/kg = 28623800\,J[/tex]

Now, we use the Carnot engine equation, we get;

[tex]\frac{Q_1}{Q_2} =\frac{T_1}{T_2}[/tex]

Therefore,

[tex]Q _2 = \frac{Q_1 T_2}{T_1}=\frac{28623800\,J \times295.5\,K }{273\,K} =30982904.39\,J[/tex]

The work on the refrigerator is given by;

[tex]W= Q_2-Q_1= 30982904.39\,J-28623800\,J=2359104.39\,J[/tex]

Hence the energy that must be applied is [tex]E=2359104.39\,J[/tex]

Learn more about Carnot engine here;

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