Acquisitive convention

Note that qc and w are both positive quantities according to the acquisitive convention, because the system is still the working fluid, not the cold chamber.)... 

The one chosen is the acquisitive convention (illustrated in Figure 7.2). If our system receives heat from the surroundings (q > 0) or has work done on itself by the surroundings (w > 0) then these are regarded as positive acquisitions. 

Figure 7.2 ACQUISITIVE convention for heat (a) and work (b) in thermodynamics. The First Law of Thermodynamics written in accordance with this convention takes the form AU = q + w, where AU is the change in internal energy of the system, q is the heat absorbed by the system from the surroundings and w is the work done on the system by the surroundings.

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