A massive piston traps a fixed amount of helium gas as shown. After being brought to point (a) the system equilibrates to room temperature. Weight is then added ADIABATICALLY compressing the gas to half of its original volume (b). Either greater than, less than, or equal to.
greater/thanless/thanequal to the pressure
Pb _________________
Pa.
greater/thanless/thanequal to The entropy of the gas at "b" is
__________________ the entropy of the gas at "a".
greater/thanless/thanequal to The temperature
Tb _________________
Ta.
greater/thanless/thanequal to The internal energy
Ub __________________
Adiabatic, reversible = isentropic.
Compressing the gas increases the pressure.
The temperature should increase, but the system remains at room
temp through the compression, so clearly heat must be leaving the
system.
So entropy must change.
dS = dQ / T; T constant, dQ < 0 (heat leaves system to keep temp
const), dS < 0
Temperature remains the same.
Internal energy: dU = T dS - p dV
dS < 0, p increases and dV < 0 :
Just guessing at this one, but it should increase, because work is
being done on the gas in excess of the heat being allowed to
escape. i.e. T dS decreasing, but -p dV > 0 increasing faster
than T dS decreasing.
Pressure necessarily increases.
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