first law of thermodynamics

Question

A system absorbs 250 J of heat and does 150 J of work. The change in internal energy of the system is:

RankGuru · Accepted Answer

According to the **First Law of Thermodynamics** (IUPAC convention):
$\Delta U = q + w$
- $q$: Heat absorbed by the system $= +250 	ext{ J}$
- $w$: Work done **by** the system $= -150 	ext{ J}$ (system losing energy to surroundings)
$\Delta U = 250 + (-150) = 100 	ext{ J}$
- The internal energy of the system increases by $100 	ext{ J}$ because heat gain exceeds work output.

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first law of thermodynamics

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