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Heat, Internal Energy And Work - Thermodynamics - Practice Questions & MCQ

Edited By admin | Updated on Sep 25, 2023 25:23 PM | #NEET

Quick Facts

  • Heat, Internal energy and Work in Thermodynamics is considered one the most difficult concept.

  • 74 Questions around this concept.

Solve by difficulty

In a given process of an ideal gas dW=0 and dQ<0. Then for the gas

Which statement is true for heat energy?

Which of the following statements is correct for any thermodynamic system?

Cooking gas containers are kept in a lorry moving with uniform speed. The temperature of the gas molecules inside will

An insulated container of gas has two chambers separated by an insulating partition. One of the chambers has volume V_{1} and contains ideal gas at pressure P_{1} and temperature T_{1} . The other chamber has volume V_{2} and contains ideal gas at pressure P_{2} and temperature T_{2} . If the partition is removed without doing any work on the gas, the final equilibrium temperature of the gas in the container will be

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A gas mixture consists of 2 moles of O2 and 4 moles of Ar at temperature T. Neglecting all vibrational modes, the total internal energy of the system is

Two thermally insulated vessels 1 and 2 are filled with air at temperatures (T_{1},T_{2}), volume (V_{1},V_{2}), and pressure (P_{1},P_{2}), respectively. If the valve joining the two vessels is opened, the temperature inside the vessel at equilibrium will be

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Concepts Covered - 1

Heat, Internal energy and Work in Thermodynamics

Quantities Involved in First Law of Thermodynamics -

(a) Heat (Q) : It is the energy that is transferred between a system and its environment because of the temperature gradient.

(b) Work (W) : Work can be defined as the energy that is transferred from one body to the other owing to a force that acts between them.

(C)  Internal energy (U) : Internal energy of a system is the energy possessed by the system due to molecular motion and molecular configuration.

         Types of internal energy - 

  • Due to molecular motion internal energy is kinetic internal energy (UK).

  • Due to molecular configuration, it is called internal potential energy (UP).


Important points :

  1. Heat and work are path dependent quantities and Internal energy is point function.

  2. \begin{array}{l}{\Delta W=P \Delta V=P\left(V_{f}-V_{i}\right)} \\ {\Delta W=\text { positive if } V_{f}>V_{i} \text { i.e. system expands against some external force. }} \\ {\Delta W=\text { negative if } V_{f}<V_{i} \text { i.e. system contracts because of some external force exerted by the surrounding. }}\end{array}

  3. The area of P-v diagram on volume axis give the work done in a reversible process. Also for quasistatic process work is given by

                                                          

                                                                         

                                                                                       W=\int_{V_{1}}^{V_{2}}P.dV

  1. And for a cyclic process the clockwise area will show positive work and anticlockwise area will show the negative work done.

  2. Internal energy of an ideal gas is totally kinetic and is given by

  U = \frac{3}{2}.n.R.T

So, Internal energy of an ideal gas is the function of temperature only.

       6. For heat transfer - 

 

               \Delta Q= mL (for change of state)

               \Delta Q= ms\Delta T (for change in temperature)

                      or,

             \Delta Q= nc\Delta T

           Where,    c = molar specific heat capacity

Sign of dQ(Heat)

dQ> 0 if heat is given to the system

dQ< 0 if heat is extracted from the system

 

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Heat, Internal energy and Work in Thermodynamics

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