5.26 For the following processes, calculate the change in internal energy of the system and determine whether the process is endothermic or exothermic.
here, heat flowed into the system (the balloon), so we have q = +850 J. the system expanded against the surroundings, and in doing so did work, so w = -382 J. by the first law,
(b) A 50 g sample of water is cooled from 30oC to 15oC, thereby losing approximately 3140 J of heat.
since heat is flowing from the system (the water) to the surroundings, q is (-) and the process is exothermic. There really isn't any work done to speak of here, so DE = q = - 3140 J.
since q = (-), the heat flows from the system to the surroundings, and the process is exothermic. We have