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5 Thermochemistry Solutions to Exercises greater than the magnitude of the quantity entering the system. In system (i), the magnitude of the heat leaving the system is less than the magnitude of the work done on the system. In system (iii), the magnitude of the work done by the system is less than the magnitude of the heat entering the system. None of the systems has 0 for all three systems. 5.5 (a). No. This distance traveled to the top of a mountain depends on the path taken by the hiker. Distance is a path function, not a state function. (b) Yes. Change in elevation depends only on the location of the base camp and the height of the mountain, not on the path to the top. Change in elevation is a state function, not a path function. 5.6 (a) State B (b) = energy difference between State A and State B. = + or = E3 + E4 (c) = energy difference between State C and State D. = - or = - (Note that the sign of E depends on the definition of initial and final state, but the magnitude is the absolute value of the difference in energy.) (d) The energy of State E is + while the energy of State is E₁ + E2. Since > State E is above State B on the diagram; State E would be the highest energy on the diagram. 5.7 (a) You, part of the surroundings, do work on the air, part of the system. Energy is transferred to the system via work and the sign of W is (+). (b) The body of the pump (the system) is warmer than the surroundings. Heat is transferred from the warmer system to the cooler surroundings and the sign of q is (-). (c) The sign of W is positive and the sign of q is negative, so we cannot absolutely determine the sign of E. It is likely that the heat lost is much smaller than the work done on the system, so the sign of is probably positive. 5.8 (a) W = -PAV. Since for the process is (-), the sign of W is (+). (b) = q + W. At constant pressure, AH = q. If the reaction is endothermic, the signs of AH and q are (+). From (a), the sign of W is (+), so the sign of is (+). The internal energy of the system increases during the change. (This situation is described by the diagram (ii) in Exercise 5.4.) 5.9 (a) The temperature of the system and surroundings will equalize, so the temperature of the hotter system will decrease and the temperature of the colder 108