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5 Thermochemistry Visualizing Concepts 5.1 The book's potential energy is due to the opposition of gravity by an object of mass m at a distance d above the surface of the earth. Kinetic energy is due to the motion of the book. As the book falls, d decreases and potential energy changes into kinetic energy. The first law states that the total energy of a system is conserved. At the instant before impact, all potential energy has been converted to kinetic energy, so the book's total kinetic energy is 71 J, assuming no transfer of energy as heat. For an object under the influence of gravity, both potential (Ep = mgd) and kinetic energy (Eₖ = 1/2 mv²) are directly proportional to mass of the object. A heavier book falling from the same shelf has greater kinetic energy when it hits the floor. 5.2 (a) The caterpillar uses energy produced by its metabolism of food to climb the twig and increase its potential energy. (b) Heat, q, is the energy transferred from a hotter to a cooler object. Without knowing the temperature of the caterpillar and its surroundings, we cannot predict the sign of q. It is likely that q is approximately zero, since a small creature like a caterpillar is unlikely to support a body temperature much different from its environmental temperature. (c) Work, W, is the energy transferred when a force moves an object. When the caterpillar climbs the twig, it does work as its body moves against the force of gravity. (d) No. The amount of work is independent of time, and therefore independent of speed (assuming constant caterpillar speed). (e) No. Potential energy depends only on the caterpillar's position, so the change in potential energy depends only on the distance climbed, not on the speed of the climb. 5.3 (a) The internal energy, E, of the products is greater than that of the reactants, so the diagram represents an increase in the internal energy of the system. (b) for this process is positive, +. (c) If no work is associated with the process, it is endothermic. 5.4 (a) For an endothermic process, the sign of q is positive; the system gains heat. This is true only for system (iii). (b) In order for to be less than 0, there is a net transfer of heat or work from the system to the surroundings. The magnitude of the quantity leaving the system is 107