CBSE Class 11-science Answered

If the volume expands (delta V = final volume - initial volume > 0), then W > 0. That is, during isobaric expansion the gas does positive work, or equivalently, the surroundings does negative work i.e. positive work is done by the gas on the surroundings.

If heat is added to the system, then Q > 0. That is, during isobaric expansion/heating, positive heat is added to the gas or system, or equivalently, the surroundings receives negative heat i.e. the gas receives positive heat from the surroundings.

If the system rejects heat i.e. heat is extracted from the system, then Q < 0. That is, during isobaric compression/cooling, negative heat is added to the gas, or equivalently, the surroundings receives positive heat. Restated, the surroundings receives positive heat from the gas.

From 4 to 1 and 1 to 2, heat is absorbed by the system and from 2 to 3 and 3 to 4, heat is rejected or extracted from the system.