Thermal Equilibrium

Thermal Equilibrium

Introduction: We have seen that if some cube of ice is kept at room temperature, the heat get transfers from surrounding into the ice cube. The temperature of the ice increases and at certain instant of time the temperature becomes equal to room temperature and the exchange of heat stops. Thus the body attain equilibrium. We are going to learn in detail about thermal equilibrium.

Thermal equilibrium is studied at macroscopic level. (Pressure, Volume, Temperature ,Mass, etc ) are the macroscopic parameter which is of interest in determining thermal equilibrium of the state.

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Case I: Consider a body having adiabatic wall, then there will be no transfer of heat as well as matter from system to surrounding hence there will be no change in temperature and state of the system. △q = 0.

If there is no change in state and property of the system, the system is said to be in thermal equilibrium.

The system in above diagram is in thermal equilibrium as there is no exchange of heat due to adiabatic wall.

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Case II : Consider two system A and B having adiabatic wall with surrounding and diathermic wall  with each other, then there will be no transfer of heat as well as matter from system to surrounding but there will be transfer of heat from system A to system B as  T_A >  T_B at t= 0 sec, hence there will be exchange of heat from system A to system B and thus change in temperature and state of the system. 

At t= T sec , T_A =  T_B hence there will be no exchange of heat from system A to system B and thus system A and system B will be in thermal equilibrium with each other.

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Zeroth Law of Thermodynamics : If system A is in thermal equilibrium with system B (T_A =  T_B) and system B is in thermal equilibrium with system C (T_B =  T_C) , then system A is in thermal equilibrium with system C (T_A =  T_C).

_{│<<<Thermodynamics}││ _{Internal energy>>>│} 

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