The figure shows a pV diagram for a gas going through a cycle from A to B to C a

Question

The figure shows a pV diagram for a gas going through a cycle from A to B to C and back to A. From point A to point B the gas absorbs 50 J of heat and finds its internal (thermal) energy has increased by 20J. Going from B to C, the internal (thermal) energy decreases by 5.0J

A. How much work was done by the gas from A to B?

B. How much heat was absorbed by the gas from B to C?

C. How much work was done by the gas going by the gas going from B to C?

Answers are A.30J B -5.0 C.0 J

Show all work please. Thank you

Explanation / Answer

A) according to first law of thermodynamics

dQ = du + dw

dq is the amount of heat energy supplied or absorbed

du is the change in internal energy

dW is the amount of work done on or by the gas

then A) work done by the gas dW = dQ-du = 50-20 = 30 J

B) since work done is w = P*dV

dV is the change in volume

from B to C the change in volume is dV = 0

then work done is W = 0 J

then dQ = dU = -5J (negative sign shows decresing in internal energy )

C) since work done is w = P*dV

dV is the change in volume

from B to C the change in volume is dV = 0

then work done is W = 0 J

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