For heat, q:
▪ +q → if the system gains, takes in, or absorbs heat or energy
▪ –q → if the system loses, evolves, gives off, or releases heat or energy
For work, w:
▪ +w → work is done on the system by the surroundings (volume: compresses)
▪ –w → work is done by the system on the surroundings (volume: expands)
Identify each of the following energy exchanges as primarily heat or work and determine whether the sign of E is positive or negative for the system.
a. Sweat evaporates from skin, cooling the skin. (The evaporating sweat is the system.)
b. A balloon expands against an external pressure. (The contents of the balloon is the system.)
c. An aqueous chemical reaction mixture is warmed with an external flame. (The reaction mixture is the system.)
Determine whether the sign of E is positive or negative for the system.
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