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Question

A loaded domestic refrigerator consumes 1.0 kW-hr of energy during a certain period. The internal energy of the system drops by 5000 kJ. The quantity of heat transferred from the system to the surrounding will be

The correct answer is

8.6 MJ

Step 1 – Electrical work input: \(W_{\mathrm{in}}=1\ \mathrm{kWh}=3600\ \mathrm{kJ}\).

Step 2 – Energy balance: With heat rejected taken as positive, \(\Delta U=W_{\mathrm{in}}-Q_{\mathrm{out}}\). Hence \(Q_{\mathrm{out}}=3600-(-5000)=8600\ \mathrm{kJ}=8.6\ \mathrm{MJ}\).

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Important Questions from First Law of Thermodynamics

  1. Heat transfer in a cyclic process are +20 kJ, -5 kJ, -10 kJ and +15kJ. Net work done for this cycle will be given by:

  2. An open system is one in which ______.

  3. A system will be in thermodynamic equilibrium only if it is in ____.

    A. Thermal equilibrium

    B. Mechanical equilibrium

    C. Chemical equilibrium

  4. The gas constant (R) is equal to the _____ of two specific heats.

  5. In a reversible adiabatic process the ration \(\left( {\frac{{{T_1}}}{{{T_2}}}} \right)\) is equal to:

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