1. as described by the first law of thermodynamics, the change in internal energy of a system is equal to a. the sum of the heat added and work performed b. the difference between the heat added and work performed c. the product of the pressure and change in volume d. the ratio of the heat added to the work performed 2. a 3.1-mole sample of an ideal gas is gently heated at constant temperature 290 k. the gas expands to 1.5 times its initial volume as its pressure decreases. what is the change in the internal energy of the gas? let the ideal-gas constant r = 8.314 j/(mol • k). a. 0 j b. 1500 j c. 3000 j d. -3000 j just give the answer no long answers