Energy balances sign convention

Accordingly, equations (8.8), (8.9) and (8.10) all represent statements of the First Law of Thermodynamics as it applies to the different scenarios above. Because of the sign convention needed (Frame 7) the equation adopts its varying forms depending on the energy balances which are taking place. 

Heat and work [10 ]. As mentioned at the beginning of the chapter, there is a sign convention for heat and work (6.15) in the energy balance (first law of thermodynamics). Can you use a different convention, for example, by calling heat negative when the temperature of the system is lower than the surroundings ... 

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