How much heat the gas gave to the environment if its internal energy decreased by 20 J and external forces did work by 15 J.

According to the first law of thermodynamics: Q = ∆U + A ‘, where Q is the amount of heat given by the gas (Q <0 J, since heat is removed from the system), ∆U is the change in the internal energy of the gas (∆U = -20 J , the gas gave heat to the environment), A ‘- the work done on the gas (A’ = 15 J, the work was done on the system). Let’s calculate the heat given off by the gas: Q = ∆U + A ‘= -20 + 15 = -5 J (“-” means that the heat was removed from the system). Answer: Gas gave 5 J of heat to the environment.