A 20 wt % solution of sulfuric acid in water is to be enriched to a 60 wt % sulfuric acid solution by adding pure sulfuric acid. a. How much pure sulfuric acid should be added? b. If the 20 wt % solution is available at 5◦C, and the pure sulfuric acid at 50◦C, how much heat will have to be removed to produce the 60 wt % solu- tion at 70◦C? How much heat will have to be added or removed to produce the 60 wt % solution at its boiling point?

To save energy, the air supply to a 2000 ft office has been shut off overnight and the room temperature has dropped to 40°f. in the morning, the thermostat is reset to 70°f and warm air at 120 f begins to flov in at 200ft'/min. the air is well mixed within the room, and an equal mass flow of air at room temperature (changing with time) is withdrawn through a return duct. the air pressure is nearly 1 atm everywhere. ignoring heat transfer with the surroundings and kinetic and potential energy effects, estimate how long it takes for the room temperature to reach 70°f. plot the room temperature as a function of time.