A system uses 49 J of energy to do work, and the change in internal energy is 58 J. How much heat was added to the system?

Use the first law of thermodynamics: the change in internal energy equals heat added minus work done by the system, ΔU = Q − W. Rearranging gives Q = ΔU + W = 58 J + 49 J = 107 J. Therefore, 107 J of heat was added to the system.

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