THE TWO PICTURES ARE DIFFERENT QUESTIONS. THE FIRST IS ADIABATICALLY AND THE SEC
ID: 1564468 • Letter: T
Question
THE TWO PICTURES ARE DIFFERENT QUESTIONS. THE FIRST IS ADIABATICALLY AND THE SECOND IS ISOBARICALLY!!!!!
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) the pressure p_b _______ p_a. the temperature T_b _______ T_a. The entropy of the gas at "b" is _________the entropy of the gas at "a", The internal energy U_b _____U_a. A massive piston traps a fixed amount of helium gas as shown. After being brought to point (a) the system equilibrates to room temperature. The gas is then added ISOBARICALLY compressing the gas to half of its original volume (b) the pressure p_b _______ p_a. The entropy of the gas at "b" is _________the entropy of the gas at "a", the temperature T_b _______ T_a. The internal energy U_b _____U_a.Explanation / Answer
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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