I use the sign convention:
- Heat absorbed by the system = q+ (positive)
- Heat evolved by the system = q− (negative)
- Work done on the system = w+ (positive)
- Work done by the system = w− (negative)
Could anyone please tell me, that volume increased in system does positive or negative work?
Answer
Volume increase in the system is due to work done by the system. Therefore W is negative using your notation. Think of it this way, work done on the system would push the system inwards, decreasing volume. Therefore a volume increase is work done by the system.
Alternatively you could reason using the formula: dU=dQ−dW (using your notation conventions, were U is internal energy, W is work and Q is heat added to the system)
dW=PdV.
Therefore
dU=dQ−PdV.
Therefore if dV (change in volume) is positive, dU (change in internal energy) is negative.
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