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If a gas expands at constant temperature, it indicates that :
A
kinetic energy of molecules remains the same
B
number of the molecules of gas increases
C
kinetic energy of molecules decreases
D
pressure of the gas increases
Detailed Solution
The average translational kinetic energy of one molecule of an ideal gas is $KE = \dfrac{3}{2}\dfrac{R}{N_A}T = \dfrac{3}{2}kT$
Here $\dfrac{R}{N_A} = k$ is the Boltzmann constant.
So $E_t \propto T$: the kinetic energy depends only on the absolute temperature.
Thus, at constant temperature, the kinetic energy of the molecules remains the same even though the gas expands.
During isothermal expansion the volume increases, so the pressure decreases (Boyle's law, $PV$ = constant); it does not increase.
The number of molecules of a fixed mass of gas does not change on expansion.
Here $\dfrac{R}{N_A} = k$ is the Boltzmann constant.
So $E_t \propto T$: the kinetic energy depends only on the absolute temperature.
Thus, at constant temperature, the kinetic energy of the molecules remains the same even though the gas expands.
During isothermal expansion the volume increases, so the pressure decreases (Boyle's law, $PV$ = constant); it does not increase.
The number of molecules of a fixed mass of gas does not change on expansion.