When two bodies A and B are in thermal equilibrium (a) the...

When two bodies $A$ and $B$ are in thermal equilibrium (a) the KE of all the molecules of $A$ and $B$ will be equal (b) the PE of all the molecules of $A$ and $B$ will be equal (c) the internal energies of the two bodies will be equal (d) the average kinetic energy of the molecules of the two bodies will be equal

When two bodies $A$ and $B$ are in thermal equilibrium
(a) the KE of all the molecules of $A$ and $B$ will be equal
(b) the PE of all the molecules of $A$ and $B$ will be equal
(c) the internal energies of the two bodies will be equal
(d) the average kinetic energy of the molecules of the two bodies will be equal

Key Concepts

Internal Energy

Internal energy is the total energy contained within a system, which includes both the kinetic energies of the molecules and the potential energies due to intermolecular forces. It is a state function that depends on the material properties and configuration of the system, and it does not necessarily become equal between different materials even when they are at the same temperature.

Molecular Kinetic Energy

Molecular kinetic energy is the energy associated with the motion of individual molecules. While the instantaneous kinetic energies of individual molecules can vary widely, the average kinetic energy across a large number of molecules is directly related to the temperature of the system.

Temperature

Temperature is a macroscopic measure that reflects the average kinetic energy of the microscopic particles in a system. It is a common indicator used to compare thermal states and plays a crucial role in determining the direction of heat flow between systems in thermal contact.

Equipartition Theorem

The equipartition theorem in statistical mechanics states that, at thermal equilibrium, energy is shared equally among all available degrees of freedom that contribute quadratically to the system's energy. This leads to the result that the average kinetic energy per degree of freedom is the same in systems at the same temperature, explaining why, in thermal equilibrium, the average kinetic energy of the molecules is equal.

Thermal Equilibrium

Thermal equilibrium refers to the state in which two or more systems in thermal contact have reached the same temperature, resulting in no net flow of heat between them. This concept underlies the zeroth law of thermodynamics and is fundamental in understanding that equal temperature implies a balance in the average molecular energy across different systems.

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